Whatsoever is not of faith, is sin

“Salvation could not come to the world without the mediation of Jesus Christ.

“God prepared a sacrifice in the gift of His own Son, who should be sent in due time to prepare a way, or open a door through which man might enter into the Lord’s presence, whence he had been cast out for disobedience. 

“By faith in this atonement or plan of redemption, Abel offered to God a sacrifice that was accepted, which was the firstlings of the flock. Cain offered of the fruit of the ground, and was not accepted, because he could not do it in faith; he could not exercise faith contrary to the plan of heaven. As the sacrifice was instituted for a type by which man was to discern the great Sacrifice which God had prepared, to offer a sacrifice contrary to that, no faith could be exercised, because redemption was not purchased in that way, nor the power of atonement instituted after that order; consequently Cain could have no faith; and whatsoever is not of faith, is sin” (Teachings of Presidents of the Church: Joseph Smith [2007], 48).