The Mu‘tazilah were the leading speculative theologians in advocating the obligation of rational inquiry and inference through the method based on accidents and bodies and its implications. They came to maintain that a person cannot attain faith without acquiring it himself. In their view, it cannot arise through necessary knowledge that Allah places in a person’s heart, nor through inspiration and guidance from Him that He grants exclusively to whomever He wills among His servants.

For this reason, those who affirm divine decree, such as al-Ash‘arī and others, disagreed with them, saying that what is known through rational inquiry can also be known by necessity. For, in their view, this is not a matter of necessity, but of the customary course of things.

The Mu‘tazilah say that if faith is a gift that Allah Most High bestows upon a servant as a favor, then the servant does not deserve any reward.

Ahl al-Sunnah say that Allah shows kindness and favor to His servant by sending him the Messenger, peace and blessings of Allah be upon him; by giving him hearing, sight, and a heart with which to understand; by guiding him to faith; and by causing him to die upon it. All of this is kindness and favor from Him toward the believer. Although He has prescribed mercy for Himself, and it is incumbent upon Him to help the believer, and His servants’ right upon Him, if they worship Him alone, is that He not punish them, this is a right He has Himself made binding, through His perfect words and by virtue of the realities of the names and attributes that His holy Essence rightfully possesses—not because any created being has imposed any obligation or prohibition upon Him.