Jacob’s marvelous chapter 9 is unsurpassed in the Book of Mormon or elsewhere. The Atonement is the first theme of redemption that he addresses (expressly in 9:7, 25, 26). What are some of the powers of the Atonement that Jacob mentioned here? There are several: the power of resurrection, the power to bring one back into the presence of God, and the power to make what was corrupted incorrupt. That is one of the main powers of at-one-ment, bringing and holding things together.
Although ancient people did not use the term entropy, the basic principle of this law of physics was understood by Jacob. Everything in nature disintegrates. As you look around, you will see decay everywhere. But the power of the Atonement arrests that entropy and reverses it, restoring each corrupted thing to its most perfect state—physically and spiritually. Beyond restoration, Christ will permanently stop the process of entropy and corruption. "If it were not so, this flesh must be laid down to rot and to crumble to its mother earth and rise no more" (9:7).
We can think of Christ as the Great High Priest, especially in regard to duties the High Priest would have performed when he officiated in the temple. The High Priest is the one who made the atoning sacrifice, and accordingly Lehi had said to Jacob: "Wherefore redemption cometh in and through the Holy Messiah for he is full of grace and truth. Behold, he offereth himself a sacrifice for sin to answer the ends of the law unto those who have a broken heart and a contrite spirit" (2 Nephi 2:6). The picture here is of the Great High Priest who not only performs the offering, but he is the offering. What more could you ask for than that?
Elder Jeffery R. Holland wrote,
Jacob’s testimony was that "the Mighty God" will always deliver "his covenant people" and that the Mighty God is, by his own divine declaration, the Lord God Jesus Christ, the "Savior … and Redeemer, the Mighty One of Jacob."
Jacob reflected on such teachings—especially those contained in the writing of Isaiah—so that his current audience and future readers "might know concerning the covenants of the Lord that he has covenanted with all the House of Israel," giving the parents of every generation cause to "rejoice" and to" lift up [their] heads forever, because of the blessings which the Lord God shall bestow upon [their children].
And then Elder Holland adds something that is key to chapter 9: "At the heart of the covenant and the reason for such rejoicing is the atoning sacrifice of that ‘Mighty God’ who is the Savior and Redeemer of the world." (Christ and the New Covenant [1997], 66–67).