One of the fundamentals of faith is the belief in the Prophets (messengers of Allah). A man cannot be considered a Muslim or a believer unless he believes that Allah sent to mankind Prophets from among themselves, who conveyed the Truth revealed to them from their Lord, Allah brought them good tidings, warned them, expounded and interpreted Allah's message for them. Hence, man will be considered a Muslim only if he believes in all prophets and that they all brought the same truth from Allah, without making distinction between any of them.
“ Say (O Muhammad): We believe in Allah and that which was revealed unto us and that which was revealed unto Abraham and Ismael and Isaac and Jacob and the tribes, and that which was vouchsafed unto Moses and Jesus and the Prophets from their Lord. We make no distinction between any of them, and unto Him we have surrendered.” (Qur'an 3:84).
Why has Allah enjoined belief in the Prophets and made it a fundamental of faith besides belief in Him, though the belief in Allah is the basis of everything? The answer is obvious. How can man know his Lord and worship Him in the right way without the Prophets and their guidance? Consider the falsehood of mankind concerning their Lord throughout history, how they imagined Him and worshipped Him in their various ages of pre-Islamic paganism. Once they imagined Him in the form of the sun's disc, as was the case with ancient Egyptians; once in the form of a superman, as did the Greeks and Romans; once in the form of a star and still another in the form on an idol. So fancies differed and all strayed from the true god because they sought guidance from their own imagination, desires and limited knowledge and didn't follow the truth in the right way as confirmed by Allah, that is through Prophets to whom the Truth had been revealed.
No less wrong was the perception of various times of ideological ignorance when there were small gods besides the Lord of lords who enjoyed some of His traits, such as a god of rain, another of lightning, another of thunder, another of the wind, another of the sea (Neptune) another of fertility, another of progeny and others of every affair of life.
If we believe that Divinity and Lordship are the major issues in the life of man and that the worship of Allah is the object of human existence as in Allah's saying:“ I created the jinn and mankind only that they might worship Me.” (Qur'an 51:56), then, we will understand why belief in the Prophets is a principal constituent of faith; for as we have seen in historical reality, it is impossible for humanity to9 be guided to the truth with regard to divinity and worship through other than the right and authorized source, that is - the prophets sent by Almighty Allah.
The same applies to the necessity of belief in all prophets without distinction whatsoever between any of them. They all came for one purpose. They were sent to make it known that there is only ONE God in the whole universe, that is Almighty Allah (Be He glorified and high exalted!) with no partner. They said to people, “ Serve Allah! Ye have no other god but Him.” (Qur'an 11:50,11:61, 11:84).
So, what is the meaning of believing in one prophet and denying another? In fact, denying any of them is the same as denying them all, since they expounded to men the same thing revealed to them by Allah.
“ We sent no messenger before thee but we inspired him (saying): There is no god Save Me (Allah), so worship Me.” (Qur'an 21:25).