Why Prophets were send?
To direct the human kind Allah sends down prophets among different nations, so they can guide people and make people aware of God existence; some are given books or revelations and/or some are given specific instructions
So why the prophets were send so people are bound by justice
57:5 His is the dominion of the heavens and earth. And to Allah are returned [all] matters. He causes the night to enter the day and causes the day to enter the night, and he is Knowing of that within the breasts. Believe in Allah and His Messenger and spend out of that in which He has made you successors. For those who have believed among you and spent, there will be a great reward. And why do you not believe in Allah while the Messenger invites you to believe in your Lord and He has taken your covenant, if you should [truly] be believers? It is He who sends down upon His Servant [Muhammad] verses of clear evidence that He may bring you out from darknesses into the light. And indeed, Allah is to you Kind and Merciful.
Also prophet’s shows miracle by the will of God to proof to the people that what they are claiming comes from the God itself for example Moses shows lots of miracles during his life time and so did Jesus, but very few people believe on their message in their life time.
Same scenario happened when Muhammad PBUH started asking people to come toward Allah and deliver the message of Quran, people asked him to show miracle but he was not given any clear Miracle as God mentioned that prophet before him were also given miracles but people deny them as well
3:184 [They are] those who said, “Indeed, Allah has taken our promise not to believe any messenger until he brings us an offering which fire [from heaven] will consume.” Say, “There have already come to you messengers before me with clear proofs and [even] that of which you speak. So why did you kill them, if you should be truthful?”
Then if they deny you, [O Muhammad] — so were messengers denied before you, who brought clear proofs and written ordinances and the enlightening Scripture.
To become a believer in Islam one has to say, “There is no God except Allah and Muhammad PBUH is last messenger and prophet”; so believing in Muhammad is essential to become a Muslim and which means one also has to believe the revelation onto him and also how he profess those teaching and which reach us through Hades and Sunnah (recorded teaching of prophet Muhammad PBUH). God send his prophets and its revelations but the last brick that completed the building of prophet hood was laid by Muhammad.
Quran 5:48, And we have revealed to you, [O Muhammad], the Book in truth, confirming that which preceded it of the Scripture and as a criterion over it. So judge between them by what Allah has revealed and do not follow their inclinations away from what has come to you of the truth. To each of you we prescribed a law and a method. Had Allah willed, He would have made you one nation [united in religion], but [He intended] to test you in what He has given you; so race to [all that is] good. To Allah is your return all together and He will [then] inform you concerning that over which you used to differ?
Quran 3:164, Certainly did Allah confer [great] favor upon the believers when He sent among them a Messenger from themselves, reciting to them His verses and purifying them and teaching them the Book and wisdom, although they had been before in manifest error.
It is obligatory on believer to look at the life of Muhammad because it is the true representation of Quran through which he brought about a revolution in life of ignorant Arabs and raise them to the best of Muslims of their time.
How it make Sense:
· Prophet-hood is a chain which started from Adam AS and ended on Prophet Muhammad PBUH, and as a believer we are not asked to distinct between them because all of them deliver the same message.
· Allah chooses prophets in a human form who live among certain community and tribe so he can convey the message effectively as he understands the language, culture and ethics of his time.
· Prophets has been given miracle by Allah so they can convince people of the message they are trying to deliver, as they claim that what they are able to accomplish is by the will of Allah but very few people put heed.
· Most of the prophets mentioned by name in quran, went through lots of struggle while delivering this message, people rejected them, punish them, tried to kill them, send them away from their community. But they kept on persisting since they are preaching the truth and decided to stand by it.
So two main reasons for sending prophets in every nation are to inform them of their creator and about a day coming after here in which they will be judged; another is to create justice among them through the book.