Prophets must be infallible
We learned that prophets have been sent to lead and direct mankind. Undoubtedly, if the leader is tainted by wrongdoing and evil, he won’t be able to direct people to chastity and purity. Therefore, prophets must be free from wrongdoing and mistakes, so that people may confidently follow them to prosperity.
In other words, if someone urges people to be truthful and trustworthy but himself is a liar or at times lapses into dishonesty and treachery, his words will never deeply sway people. Similarly, if divine prophets had not been free from error and mistakes, and people had anticipated that they would make mistakes in carrying out their mission, they would never have wholeheartedly believed his words. Consequently, a complete compliance would not have occurred and their objectives would not have been achieved.
Indeed, God won’t choose anyone who is not free from idolatry and wrongdoing to deliver His message. Rather, He would pick those who are free from any impurity whatsoever and would maintain this infallibility in the future to assume this lofty position.
Prophets must perform miracles
Anyone with a healthy nature, won’t accept any claim without any reason, and if someone buys a claim without compelling reasons, this reveals his lack of common sense. Therefore, it is inevitable that prophets should present some evidence to prove the authenticity of their prophetic mission as well as the fact that they are sent by God.
One of the emblems that establish the prophets’ connection with the Unseen is miracles. Miracle signifies something that could not be performed by others except the prophets. For example, reviving the dead or curing incurable diseases. With regard to this, Imām al-Ṣādiq (‘a) has said, “Any prophet should present some proof of his honesty.” And one of the most manifest proofs is miracles through which people can establish the authenticity of anyone who claims to be a prophet.
 This has been deduced from a narration from Imām al-Riḍā cited in ‘Uyūn Akhbār ar-Riḍā, vol. 2, Qum, p.125.
 ‘Uṣūl al-Kāfī, vol. 1, p. 168. It is likely that the word ‘alam be read as ‘ilm.