Having reached the end of the first major section of the first part of Romans, 5:1 serves as triumphant conclusion to that section and an introduction to the next major section, chs.5-8.
“Therefore.” When Paul writes “therefore” it’s always good to ask what it’s there for because it’s there for a reason. And that reason is often the conclusion to what has gone before. And so it is here. V.1 brings the first four chapters to its intended conclusion.
The conclusion to all this (chs.1-4), Paul says, is that “we” (both Jew and Gentile gathered together in sin, chs.1-3) “have been made” (note the passive voice) “righteous” (restored to right relation to God) “through his faithfulness” (apart from the Law; through Christ’s life of loyalty and love offered to God) and now “have” (textual evidence is evenly divided on whether the verb is an indicative [stating a fact] or an exhortation [to do something] but context seems to favor an indicative as here in the CEB) “peace with God” (“shalom,” God’s design for human flourishing, beginning with right relation to God and encompassing every other aspect of life in the world) “through our Lord Jesus Christ” (Christ = Messiah).
God’s plan was always to have a world full of people living in closest friendship with him, a family sharing life together on this planet. Once we revolted and chose to live otherwise, by ourselves, for ourselves, and through our own power and wisdom, God began a counter-revolutionary movement to rectify and restore his creatures and creation to his divine intention. Jesus Christ is the center and key to God’s strategy. That’s why Paul spends the first four chapters of this letter establishing just this point: apart from the Law, through the faithfulness of Jesus Christ, we are reclaimed and restored for God and his purposes for us.
In the remainder of this paragraph Paul begins to spell out the implications of this.