How did the Almighty chose His Prophets. What was the criteria of His selection?
The Almighty selects a Rasūl on the basis of His all embracing wisdom and sagacity. The basic criterion is that people who have a very exceptional moral character are chosen for this great task. They are the ones who lead unblemished lives before they are called to serve Allah. The Almighty selects them as messengers only after they exhibit a high moral character. The Qur’ān refers to this aspect of their lives as ‘Bayyinah’(a clear sign):
Can those who are on a clear sign from their Lord, and then a witness also comes to them from Him and before this, the Book of Moses is already present as a guide and a mercy and those who are without any insight be equal? (11:17)
The above quoted verse is about Muhammad (sws). About Noah (sws), the Qur’ān says:
He said: ‘O my People! Tell me if I am on a clear sign from my Lord, and moreover He also specially blessed me with His mercy, but that the Mercy has been obscured from your sight? Shall we compel you to accept it when you are averse to it? (11:28)
About Sālih (sws), the Qur’ān says:
He said: ‘O my People! Tell me if I am on a clear sign from my Lord, and, moreover, He also blessed me with His mercy – who then can help me against Allah if I were to disobey Him? (11:63)
About Shu‘ayb (sws), the Qur’ān says:
He said: ‘O my People! Tell me if I am on a clear sign from my Lord, and moreover He also specially blessed me with His sustenance [pure and] good as from Himself? I wish not, in opposition to you, to do that which I forbid you to do. (11:88)
In these verses, a mention of ‘Bayyinah’ (clear sign) precedes the mention of Wahi (revelation) for which the words ‘witness’, ‘mercy’ and ‘pure sustenance’ are used. This shows that it is only after those chosen to become Messengers have polished and refined their inner-self that they become the recipients of divine revelation.