Second Nephi 2:8

Wherefore, how great the importance to make these things known unto the inhabitants of the earth, that they may know that there is no flesh that can dwell in the presence of God, save it be through the merits, and mercy, and grace of the Holy Messiah, who layeth down his life according to the flesh, and taketh it again by the power of the Spirit, that he may bring to pass the resurrection of the dead, being the first that should rise.

Because of our flesh, we make mistakes and sin. Those sins keep us from God. Through Christ's atoning sacrifice, he can remove our sins and give us hope that we can still return to God. This is the doctrine of the Atonement and redemption.