3 Nephi 12:19

And behold, I have given you the law and the commandments of my Father, that ye shall believe in me, and that ye shall repent of your sins, and come unto me with a broken heart and a contrite spirit. Behold, ye have the commandments before you, and the law is fulfilled.

The law of the gospel is simple to understand. The law, however, cannot be kept without gifts from God. Belief and faith in Christ are gifts. Repentance is a gift of the Christ's atonement. We cannot come fully unto Christ without the gift of the Holy Ghost. Nor can we manufacture a broken heart and a contrite spirit. God in his mercy gives us the law of happiness and then provides the gifts and means to keep it. Our test is whether we will choose his way and then ask for help.

Alma 42:23

But God ceaseth not to be God, and mercy claimeth the penitent, and mercy cometh because of the atonement; and the atonement bringeth to pass the resurrection of the dead; and the resurrection of the dead bringeth back men into the presence of God; and thus they are restored into his presence, to be judged according to their works, according to the law and justice.

When we repent, we can receive mercy. Christ can offer us mercy because of his suffering and death through the atonement. Because he died as the final sacrifice of the atonement, he could exercise the keys of the resurrection, first for himself and then for the rest of us. The resurrection restores not only our physical bodies, but it restores us to the presence of the Father. Whether we get to remain in his presence depends on what we did with our lives and what we have become. God will apply justice in his judgment, but we need not fear justice if we have applied for mercy through the atonement. Mercy will be applied first, and only those who refuse mercy will have to face justice straight on. Christ saves us from sin, from ourselves, and from the grasp of justice that otherwise would banish us from the Father's presence forever.