the prophetic mission
The third primary principle is the faith in the prophetic mission of the prophets who were sent by God to guide and lead mankind and as some sources suggest the number of these prophets amounts to 124,000. The last prophet after whom no other prophet has come or will ever come is Muhammad ibn ‘Abdullāh (may God bless him and his household) who introduced Islam.
The necessity of the appointments of prophets
It is evident that the All-wise Creator did not create this vast universe in vain and also it is obvious that the goal behind creation is not profitability because as we noted previously God is free from any defect and need and so He did not create the world to fulfill His needs and complement Himself. Consequently, the objective behind creation must have to do with the creatures. And the only objective that one could imagine for this world is the evolution and perfection of the creatures, especially the all-out evolution of mankind. Now, this question arises that how and by what means this all-out evolution could be accomplished?
It is manifest that the evolution and progress of mankind is not practicable without a divine plan and instructor. Because earthly leaders due to their limited knowledge and perceptions could not direct mankind accurately, and since they are not free from error and mistake and their judgments are erroneous, they are not qualified to assume leadership unless they follow heavenly leaders.
But the divine leaders, thanks to their connection with the Unseen and their freedom from error and mistakes can direct mankind toward genuine prosperity without lapsing into error in their leadership.
Given what was said earlier, one realizes that mankind’s plan must have been developed by the Creator who is aware of all their needs and also knows that what is harmful and beneficial for them. And these divine plans are delivered by those who are qualified for the prophetic mission and are in touch with the Unseen.
Man is social
Every one believes that man is social, that is, he can not keep on living on his own but has to live with other people. And this co-existence builds up the society. Undoubtedly, this way of life will lead to differences and enmities. If there were no accurate and fair law to manage the society, the society would not advance on the path of progress and prosperity.
Therefore, the vital significance of a solid, accurate, and fair law to guard the rights of the society and individuals is evident. Now the question is who should draw up this law? Who is the best law-maker? And what are his qualifications?
The first qualification is that the law-maker should be aware of the mental, physical, emotional and instinctive traits of those to whom the law would be applied and such perfect awareness is not possible for anyone except God, because He is the creator and only He is truly aware of the internal as well as the external dimensions of mankind and their mental and physical peculiarities. Only God is cognizant of the various incidents happening in man’s life and the developments occurring in the society and therefore, only He is able to draw up a perfect plan for man’s life and keep him from annihilation.
God, the Exalted, has presented this plan through outstanding and eminent men picked from among people, who are free from error, so that man may achieve his all-out evolution by seeking guidance from this plan.
Another function performed by the prophets is that they are the first to apply the divine law, that is, besides delivering the law, they teach men to practice the law. They are the visible embodiments of that law so that others choose the divine law as the plan for their lives by modeling them. Therefore, the faithful people believe that God has sent prophets to direct men toward the path of evolution and felicity in every era.
Someone asked Imām aṣ-Ṣādiq (‘a) “Why prophets are appointed?”
The revered Imām replied, “having proven with irrefutable arguments the existence of an All-wise Creator who has brought us form non-being to being and having established that God is not material and is superior to every other creature, and none can see or observe Him, so that he might talk to Him about the state of affairs, and put his questions to Him, therefore, it is inevitable that He must have messengers and prophets who guide people toward felicity and explain what is harmful for them and in every era, there must be a guide among people so that earth is not bereft of God’s proof.”
 ‘Uṣūl al-Kāfī, vol. 2, p. 168.