2 Corinthians 5:17 - Ellicott's Commentary On The Whole Bible

Therefore if any man be in Christ. — To be in Christ, in St. Paul’s language, is for a man to be united with him by faith and by baptism (Romans 6:3-4), to claim personally what had been secured to him as a member of the race for whom Christ died. In such a case the man is born again (Titus 3:5) — there is a new creation; the man, as the result of that work, is a new creature. The old things of his life, Jewish expectations of a Jewish kingdom, chiliastic dreams, heathen philosophies, lower aims, earthly standards — these things, in idea at least, passed away from him at the time when he was united with Christ. We may trace an echo of words of Isaiah’s that may have floated in the Apostle’s memory: “Remember ye not the former things, neither consider the things of old. Behold I make new things” (Isaiah 43:18-19). The words in italics are in the LXX. the same as those which St. Paul uses here.