Mosiah 3 contains an account of the atonement as described by an angel of God. Missing from this account are most of the sort of things that members these days will say when they think of the atonement. In fact, it tells a completely different story. The story in Mosiah 3 is one of becoming a saint. It is a story of change. It is a story of requirements. Yes, it offers forgiveness. But it primarily speaks of forgiveness in the context of ignorance, and sharply warns those who knowingly break the commandments. And, to be certain, it only offers forgiveness for knowingly breaking the commandments on condition of repentance.
It is a story of transformation of the individual by which they become a saint through the atonement of Christ.
Mosiah 3:18 For behold he judgeth, and his judgment is just; and the infant perisheth not that dieth in his infancy; but men drink damnation to their own souls except they humble themselves and become as little children, and believe that salvation was, and is, and is to come, in and through the atoning blood of Christ, the Lord Omnipotent.
19 For the natural man is an enemy to God, and has been from the fall of Adam, and will be, forever and ever, unless he yields to the enticings of the Holy Spirit, and putteth off the natural man and becometh a saint through the atonement of Christ the Lord, and becometh as a child, submissive, meek, humble, patient, full of love, willing to submit to all things which the Lord seeth fit to inflict upon him, even as a child doth submit to his father.
According to the words of the angel, the entire point of the atonement is one of becoming a saint through the atonement.
When members these days gush in sacrament meeting about the atonement, they mostly start talking about the atonement as excusing sin. Sure, they do include forgiveness from sin. But they usually speak about the atonement as excusing them from their current sins as well. They speak of the atonement with the gratitude of the excused. They speak of it not in gratitude that they can repent and be forgiven, but more earnestly that they can be the way they are and, thanks to the atonement, still gain heaven. They do not recognize at all that they are not clean of anything they still indulge in, and in fact they openly gush in gratitude for the opposite.
And such a doctrine is completely wrong. It is only through change that Christ has power to forgive. He will not forgive us in our sins, because he saves us from them by requiring repentance, and offering forgiveness on condition of repentance. But there is no forgiveness for that which is still part of our daily misbehavior.
Helaman 5:10 And remember also the words which Amulek spake unto Zeezrom, in the city of Ammonihah; for he said unto him that the Lord surely should come to redeem his people, but that he should not come to redeem them in their sins, but to redeem them from their sins.
11 And he hath power given unto him from the Father to redeem them from their sins because of repentance; therefore he hath sent his angels to declare the tidings of the conditions of repentance, which bringeth unto the power of the Redeemer, unto the salvation of their souls.
Thus is it though repentance that we are forgiven, and only through repentance that we gain access to Christ's forgiveness.
Think about it. Compare the sermon on the mount with the modern, misguided picture of how the atonement works.
Christ makes no mention of his redemption for sin in the sermon on the mount. Instead he preaches righteousness and obedience. Those who think Christ condemned the Pharisees for over-strict obedience have never honestly read the sermon on the mount. For Christ required a level of gospel living in his teachings which far exceeds our daily practice.