What the texts say. With echomen (omicron), Paul states a fact: having been justified by faith, we have peace with God through our Lord Jesus Christ. With echōmen (omega), he gives an exhortation: let us have, or let us enjoy, that peace. By the early centuries of the Church the two vowels were pronounced alike, so a scribe copying by ear could write either (Very Strong).
The manuscript evidence. “Let us have” is read by the first hands of Codex Sinaiticus and Codex Vaticanus, by Codex Alexandrinus, Codex Ephraemi and Codex Claromontanus, by many other manuscripts, and by the Latin and Bohairic Coptic versions. “We have” is read by later correctors of Sinaiticus and Vaticanus, by other important witnesses, and by many later manuscripts; the earliest witness of all, a small third-century fragment (0220), appears to read “we have.” On manuscript weight alone “let us have” is ahead. Nestle’s critical text of 1904 printed it.
Why most scholars choose “we have.” The argument of Romans 5 favours a statement. Paul is describing what God has already done; verse 10 says plainly that, being reconciled, we shall be saved by his life. As C. E. B. Cranfield observed, Paul would hardly urge readers to secure a peace he has not yet shown them to have. Most modern critical editions and translations therefore read “we have” (Strong, but the external evidence keeps the question open: Debated).
What the Orthodox Church reads. The Patriarchal Text, with the Byzantine tradition, reads “we have peace.” Orthodox theology has no stake in suppressing the other reading: peace with God is a gift received in Christ and also a life to be lived and guarded. Both readings fit that faith.
How translations handle it. The KJV, ASV, NKJV, ESV, NIV, NRSVUE, RSV Catholic Edition and Reina-Valera 1909 read “we have peace,” the modern ones usually with a note “let us have.” The Douay-Rheims, following the Latin habeamus, reads “let us have peace.”
What it does and does not change. This variant is sometimes dragged into debates about justification, but it does not settle them. Both readings begin “being justified by faith,” and both trace peace with God to “our Lord Jesus Christ.” The question is whether Paul is declaring the gift or urging his readers to live in it, and he does both in the same letter.