People are more than just minds or hearts. We are complex beings with many faculties, including the mind, intellect, heart, and soul. All of our faculties, even the innermost ones, require satisfaction. The Prophets addressed all of them.
Those taught by the Prophets acquired certainty, and their view of things differed from those with limited external sight and devoid of insight and spiritual vision. Their conviction of religious truths was unshakable, and they were continually fed with Divine Revelation. They combined speech with action, knowledge with practice, and action with contemplation. 'Ali ibn Abi Talib, among others, would say: "If the veil of the Unseen were lifted up, my certainty would not increase."  There was no further degree of certainty left for them to attain.
The education given by the Prophets to their disciples, or the function of the Prophets, is described precisely: We have sent among you, of yourselves, a Messenger, to recite Our signs to you and to purify you, and to teach you the Book and Wisdom, and to teach you what you know not (2:151).