My little children, of whom I travail in birth again until Christ be formed in you,
My little children (1 Timothy 1:18; 2 Timothy 2:1; 1 John 2:1). My relation to you is not merely that of one zealously courting you (Galatians 4:17-18), but that of a father to his children (1 Corinthians 4:15).
I travail in birth - i:e., like a mother in pain until her child is born.
Again - a second time. A long-continued travail. The former time was when I was "present with you" (Galatians 4:18; note, Galatians 4:13).
Christ be formed in you - that yon may live only Christ, think only Christ (Galatians 2:20; Ephesians 3:17), and glory only in Him. His death, resurrection, and righteousness (Philippians 3:8-10; Colossians 1:27).