What is the Atonement of Jesus Christ? It is, in short, that suffering endured, that power displayed, and that love manifested by the Savior in three principal locations, namely, the Garden of Gethsemane, the cross of Calvary, and the tomb of Arimathaea. In a larger sense, the Atonement commenced when the Savior made that selfless offer in the premortal council, "Here am I, send me" (Abraham 3:27), and continues without end as he "bring[s] to pass the immortality and eternal life of man" (Moses 1:39).
There are at least three principal purposes of the Atonement:
First: To restore all that was lost by the fall of Adam. This was done by (1) bringing about the resurrection for all men, thus overcoming physical death (see 1 Corinthians 15:21–22); and (2) restoring all men to the presence of God for the purpose of being judged, thus overcoming what the scriptures call a first spiritual death (see Helaman 14:16; D&C 29:41). Both of these deaths were imposed upon all men because of Adam; both of these deaths were overcome for all men through Christ.
Second: To provide for the possibility of repentance so that men might be cleansed from their individual sins and by so doing overcome what the scriptures call a second spiritual death (see Helaman 14:18).
Third: To provide the power necessary to exalt us to the status of a god (see D&C 76:69).
These three purposes are designed to help us permanently return to God's presence and become like Him.