what is the significance of surah II and ayat 255? is there any proof of the greatness of this surah?

Praise be to Allaah. 

Imaam Ibn Katheer (may Allaah have mercy on him) said in his Tafseer of Aayat al-Kursiy from Soorat al-Baqarah:

 This is Aayat al-Kursiy, which has a high status. It was reported in a saheeh hadeeth from the Messenger (peace and blessings of Allaah be upon him) that it is the greatest aayah in the Book of Allaah… It was narrated from Ubayy, i.e., Ubayy ibn Ka’b that the Prophet (peace and blessings of Allaah be upon him) asked him which aayah in the Book of Allaah was the greatest. He said, “Allaah and His Messenger know best.” He repeated it several times, then he said, “Aayat al-Kursiy.” The Prophet (peace and blessings of Allaah be upon him) said, “Congratulations upon your knowledge O Abu’l-Mundhir. By the One in Whose hand is my soul, it has a tongue and two lips, and it glorifies the Sovereign (i.e., Allaah) at the foot of the Throne.” This was also narrated by Muslim, without the phrase “By the One in Whose hand is my soul…”.

 It was narrated from ‘Abd-Allaah ibn Ubayy ibn Ka’b that his father told him that he had a vessel in which he kept dates. He used to check on it and found that the number was decreasing. So he kept guard on it one night and saw a beast that looked like an adolescent boy. He said: “I greeted him with salaams and he returned my greeting, then I asked him, ‘What are you, a jinn or a human?’ He said, ‘A jinn.’ I said to him, ‘Show me your hand.’ So he showed me his hand, and it looked like a dog’s paw with dog’s fur. I said, ‘Do all the jinn look like this?’ He said, ‘I know no one among the jinn who is stronger than I.’ I said, ‘What made you do what you did [i.e., taking the dates]?’ He said, ‘We heard that you are a man who loves charity, and we wanted to have some of your food.’” Ubayy asked him, “What will protect us from you?” He said, “This aayah, Aayat al-Kursiy.” Then the next day he [Ubayy] went to the Prophet (peace and blessings of Allaah be upon him) and told him (about what had happened) and he said, “The evil one spoke the truth.”…

 Imaam Ahmad narrated: Muhammad ibn Ja’far told us, ‘Uthmaan ibn ‘Itaab told us, he said: I heard Abu’l-Sulayl saying: a man from among the companions of the Prophet (peace and blessings of Allaah be upon him) addressed the people until a large number had gathered around him, then he climbed onto the roof of a house and addressed the people, saying: “The Messenger of Allaah (peace and blessings of Allaah be upon him) said, ‘Which aayah of the Qur’aan is the greatest?’ A man said, ‘ “Allaah! Laa ilaaha illa Huwa (none has the right to be worshipped but He), the Ever Living, the One Who sustains and protects all that exists…” [al-Baqarah 2:255 – Aayat al-Kursi – interpretation of the meaning].’ He said: he put his hand between my shoulders and I felt coolness in the centre of my chest, or he put his hand on the centre of my chest and I felt coolness between my shoulders, and he said, ‘Congratulations on your knowledge, O Abu’l-Mundhir.”

 It was narrated that Abu Dharr (may Allaah be pleased with him) said: “I came to the Prophet (peace and blessings of Allaah be upon him) whilst he was in the mosque and sat down. He said, ‘O Abu Dharr, did you pray?’ I said, ‘No.’ He said, ‘ Get up and pray.’ So I got up and prayed, then I came and sat down. He said, ‘O Abu Dharr, seek refuge with Allaah from the devils of men and jinn.’ I said, ‘O Messenger of Allaah, are there devils among men?’ He said, ‘Yes.’ I said, ‘O Messenger of Allaah, what about salaah?’ He said, ‘It is the best, so let whoever wants to, do a little of it and let whoever wants to, do more of it.’ I said, ‘O Messenger of Allaah, what about fasting?’ He said, ‘It is obligatory and it is good, and the reward with Allaah is greater.’ I said, ‘O Messenger of Allaah, what about sadaqah (charity)?’ He said, ‘Allaah multiplies it many times over.’ I said, ‘O Messenger of Allaah, what (charity) is best?’ He said, ‘What a person gives at times of hardship, or what he gives in secret to a poor person.’ I said, ‘O Messenger of Allaah, which of the Prophets was first?’ He said, ‘Adam.’ I said, ‘O Messenger of Allaah, was he a Prophet?’ He said, ‘Yes, a Prophet to whom Allaah spoke.’ I said, ‘O Messenger of Allaah, how many Messengers are there?’ He said. ‘Three hundred and umpteen, a great crowd.’ And once he said, ‘(Three hundred and) fifteen.’ I said, ‘O Messenger of Allaah, what is the greatest thing that has been revealed to you?’ He said, ‘Aayat al-Kursiy, “Allaah! Laa ilaaha illa Huwa (none has the right to be worshipped but He), the Ever Living, the One Who sustains and protects all that exists…” [al-Baraqah 2:255 – interpretation of the meaning].’” (Narrated by al-Nasaa’i).

 Al-Bukhaari narrated that Abu Hurayrah said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) appointed me to guard the Ramadaan zakaah. Someone came and started taking some of the food. I grabbed hold of him and said, ‘I am going to take you to the Messenger of Allaah (peace and blessings of Allaah be upon him)!’ He said, ‘Let me be, for I am in need and I have children and am in great need.’ So I let him go. The following morning, the Prophet (peace and blessings of Allaah be upon him) said, ‘O Abu Hurayrah, what did your prisoner do last night?’ I said, ‘O Messenger of Allaah, he complained of being in great need and having children to look after, so I took pity on him and let him go.’ He said, ‘But he was lying, and he will be back.’ So I knew that he would come back, because of what the Messenger of Allaah (peace and blessings of Allaah be upon him) had said. I lay in wait for him, and he came and started taking some of the food. I grabbed hold of him and said, ‘I am going to take you to the Messenger of Allaah (peace and blessings of Allaah be upon him)!’ He said, ‘Let me be, for I am in need and I have children. I will not come back again.’ So I took pity on him and let him go. The following morning, the Prophet (peace and blessings of Allaah be upon him) said, ‘O Abu Hurayrah, what did your prisoner do last night?’ I said, ‘O Messenger of Allaah, he complained of being in great need and having children to look after, so I took pity on him and let him go.’ He said, ‘But he was lying, and he will be back.’ So I lay in wait for him on the third night, and he came and started taking some of the food. I grabbed hold of him and said, ‘I am going to take you to the Messenger of Allaah (peace and blessings of Allaah be upon him)! This is the third and last time. You said that you would not come back, then you did come back.’ He said, ‘Let me go, and I will teach you some words by which Allaah will benefit you.’ I said, ‘What are they?” He said, ‘When you lie down in your bed, recite Aayat al-Kursiy, “Allaah! Laa ilaaha illa Huwa (none has the right to be worshipped but He), the Ever Living, the One Who sustains and protects all that exists…” [al-Baraqah 2:255 – interpretation of the meaning] until the end of the aayah, then you will have a protector from Allaah and no shaytaan (devil) will come near you until morning comes.’ Then I let him go. The following morning, the Prophet (peace and blessings of Allaah be upon him) said, ‘What did your prisoner do last night?’ I said, ‘O Messenger of Allaah, he claimed that he would teach me some words by which he said Allaah would benefit me, then I let him go.’ He asked, ‘What are they?’ I said, ‘He told me, when you lie down in your bed, recite Aayat al-Kursiy, from the beginning to the end of the aayah, “Allaah! Laa ilaaha illa Huwa (none has the right to be worshipped but He), the Ever Living, the One Who sustains and protects all that exists…” [al-Baraqah 2:255 – interpretation of the meaning]. And he told me, you will have a protector from Allaah and no shaytaan (devil) will come near you until morning comes.’ And they [the Sahaabah] were always keen to do good.’ The Prophet (peace and blessings of Allaah be upon him) said: ‘He indeed told you the truth, although he is a liar. Do you know who you have been speaking with for the past three nights, O Abu Hurayrah?’ I said, ‘No.’ He said, ‘That was a shaytaan (a devil).’”

 According to another report, “… ‘I was taking food to a very poor family among the jinn.’ So he let him go, and he came back on the second night and then the third night. I said, ‘Did you not promise me that you would not come back? I will not leave you today until I bring you to the Prophet (peace and blessings of Allaah be upon him).’ He said, ‘Do not do that. If you let me go, I will teach you some words which, if you say them, no one among the jinn, great or small, male or female, will come near you.’ He said, ‘Will you do that?’ He said, ‘Yes.’ He said, ‘What are they?’ He said, ‘“Allaah! Laa ilaaha illa Huwa (none has the right to be worshipped but He), the Ever Living, the One Who sustains and protects all that exists…” [al-Baraqah 2:255 – interpretation of the meaning], and recited Aayat al-Kursiy until the end. So he let him go and he went away and did not come back. Abu Hurayrah told the Prophet (peace and blessings of Allaah be upon him) about that, and the Messenger of Allaah (peace and blessings of Allaah be upon him) said to him: “Did you not know that before?” This was narrated by al-Nasaa’i from Ahmad ibn Muhammad ibn ‘Ubayd-Allaah from Shu’ayb ibn Harb from Ismaa’eel ibn Muslim from Abu’l-Mutawakkil from Abu Hurayrah. We have noted above that something similar happened to Ubayy ibn Ka’b, so these are three separate incidents. Abu ‘Ubayd said in Kitaab al-Ghareeb: Abu Mu’aawiyah told us, from Abu ‘Aasim al-Qaffi, from al-Shu’bi from ‘Abd-Allaah ibn Mas’ood, who said: “A man from among the humans went out and was met by a man from among the jinn, who said, ‘Will you wrestle with me? If you throw me to the ground I will teach you an aayah which, if you recite it when you enter your house, no shaytaan will enter.’ So he wrestled with him and threw him to the ground. He said, ‘I see that you are very small and your forearms are like the front paws of a dog. Are all the jinn like this, or only you?’ He said, ‘I am strong among them. Let us wrestle again.’ So they wrestled again and the human threw him to the ground. So he (the jinn) said, ‘Recite Aayat al-Kursiy, for no one recites it when he enters his house, but the Shaytaan leaves, farting like a donkey.’” It was said to Ibn Mas’ood, “Was that man ‘Umar?” He said, “Who else could it have been, other than ‘Umar?” …

 It was narrated from Abu Hurayrah that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “In Soorat al-Baqaraah there is an aayah which is the best of all the aayahs of the Qur’aan. It is never recited in a house but the Shaytaan leaves: Aayat al-Kursiy.” This was also narrated via another isnaad, from Zaa’idah from Hakeem ibn Jubayr. Then he said, its isnaad is saheeh although they [al-Bukhaari and Muslim] did not narrate it. It was also narrated by al-Tirmidhi from the hadeeth of Zaa’idah, with the wording, “Everything has its pinnacle and the pinnacle of the Qur’aan is Soorat al-Baqarah. In it there is an aayah which is the greatest in the Qur’aan: Aayat al-Kursiy.” Then he said: (it is) ghareeb, we do not know it except from the hadeeth of Hakeem ibn Jubayr. Shu’bah discussed it and classed it as da’eef (weak). It was also classed as da’eef by Ahmad, Yahyaa ibn Mu’een and other imaams. Ibn Mahdi classed it is matrook and al-Sa’di classed it as false.

 It was narrated from Ibn ‘Umar that ‘Umar ibn al-Khattaab went out one day to some people who had prepared a meal. He said, “Who among you can tell me which is the greatest aayah in the Qur’aan?”  Ibn Mas’ood said, “You are asking one who knows. I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say, ‘The greatest aayah in the Qur’aan is ‘Allaah! Laa ilaaha illa Huwa (none has the right to be worshipped but He), the Ever Living, the One Who sustains and protects all that exists…’ [al-Baraqah 2:255 – interpretation of the meaning].”

 Concerning the fact that it includes the greatest name of Allaah, Imaam Ahmad said: “It was narrated that Asmaa’ bint Yazeed ibn al-Sakan said: ‘I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say about these two aayahs (interpretation of the meanings) -- “Allaah! Laa ilaaha illa Huwa (none has the right to be worshipped but He), the Ever Living, the One Who sustains and protects all that exists…” [al-Baraqah 2:255] and “Alif-Laam-Meem. [These letters are one of the miracles of the Qur’aan, and none but Allaah (Alone) knows their meanings.] Allaah! Laa ilaaha illa Huwa (none has the right to be worshipped but He), Al-Hayyul-Qayyoom (the Ever Living, the One Who sustains and protects all that exists)” [Aal ‘Imraan 3:1-2] – that they contain the greatest name of Allaah.’” This was  also narrated by Abu Dawood from Musaddid and by al-Tirmidhi from ‘Ali ibn Khashram, and by Ibn Maajah from Abu Bakr ibn Abi Shaybah, all three of them narrating from ‘Eesa ibn Yoonus from ‘Ubayd-Allaah ibn Abi Ziyaad . Al-Tirmidhi said: it is saheeh hasan.

 It was narrated in a marfoo’ report that Abu Umaamah said: “The greatest name of Allaah, which if He is called by it, He responds, is in three (soorahs): Soorat al-Baqarah, Aal ‘Imraan and Ta-Ha.” Hishaam, i.e., Ibn ‘Ammaar, the khateeb of Damascus, said: “In al-Baqarah, it is ‘Allaah! Laa ilaaha illa Huwa (none has the right to be worshipped but He), the Ever Living, the One Who sustains and protects all that exist’  [al-Baraqah 2:255 – interpretation of the meaning]. In Aal ‘Imraan it is ‘Alif-Laam-Meem. [These letters are one of the miracles of the Qur’aan, and none but Allaah (Alone) knows their meanings.] Allaah! Laa ilaaha illa Huwa (none has the right to be worshipped but He), Al-Hayyul-Qayyoom (the Ever Living, the One Who sustains and protects all that exists)’ [Aal ‘Imraan3:1-2 – interpretation of the meaning]. And in Ta-Ha it is ‘And (all) faces shall be humbled before (Allaah), Al-Hayyul-Qayyoom (the Ever Living, the One Who sustains and protects all that exists)’ [Ta-Ha 20:111].”

 Concerning the virtue of reciting this aayah after the prescribed prayers, it was narrated that Abu Umaamah said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Whoever recites Aayat al-Kursiy immediately after each prescribed prayer, there will be nothing standing between him and his entering Paradise except death.” This is how it was narrated by al-Nasaa’i in al-Yawm wa’l-Laylah, from al-Hasan ibn Bishr. It was also narrated by Ibn Hibbaan in his Saheeh from Muhammad ibn Humayr, who is al-Homsi, and is also one of the men of al-Bukhaari. The isnaad meets the conditions of al-Bukhaari.

 And Allaah knows best.