Martin Luther claimed verses 21-26 were, "the chief point, and the very central place of the Epistle, and of the whole Bible."

"God presented Christ as a sacrifice of atonement" (v.25)
F. F. Bruce summarizes it by saying, “Paul has [used] the language of the lawcourt (‘justified’), the slave-market (‘redemption’) and the altar (‘atoning sacrifice’) in the attempt to do justice to the fullness of God’s gracious act in Christ. Pardon, liberation, atonement—all are made available to men and women by His free initiative and may be appropriated by faith.”

God is just and the justifier.
"There can be no gospel unless there is such a thing as a righteousness of God for the ungodly. But just as little can there be any gospel unless the integrity of God’s character be maintained. The problem of the sinful world, the problem of all religion, the problem of God in dealing with a sinful race, is how to unite these two things. The Christian answer to the problem is given by Paul in the words: ‘God presented Christ as a sacrifice of atonement, through the shedding of his blood – to be received by faith.’” (James Denney)

In Summary...
1. Salvation doesn’t come from your ethnicity, heritage or religious practices.
2. Having a knowledge of God is a position of special responsibility, not special privilege.
3. All have sinned and all are justified freely by His grace.
4. God is both just and justifier because He sent Jesus to pay the penalty for sin.