Now I rejoice (νυν χαιρομεν). This is not a new note for Paul. See him in jail in Philippi (Acts 16:25) and in 2 Corinthians 11:16-33; Romans 5:3; Philippians 2:18.

Fill up on my part (ανταναπληρω). Very rare double compound verb (here only in N.T.) to fill (πληροω) up (ανα), in turn (αντ). It is now Paul's "turn" at the bat, to use a baseball figure. Christ had his "turn," the grandest of all and suffered for us all in a sense not true of any one else. It is the idea of balance or correspondence in αντ as seen in Demosthenes's use of this verb (De Symm., p. 282), "the poor balancing the rich." And yet Christ did not cause suffering to cease. There is plenty left for Paul and for each of us in his time.

That which is lacking (τα υστερηματα). "The left-overs," so to speak. Late word from υστερεω, to come behind, to be left, to fail. See Luke 21:4; 1 Thessalonians 3:10; 2 Corinthians 8:14; 2 Corinthians 9:12.

For his body's sake (υπερ του σωματος αυτου). As Paul showed in his exultation in suffering in 2 Corinthians 11:16-33, though not in the same sense in which Christ suffered and died for us as Redeemer. Paul attaches no atoning value whatever to his own sufferings for the church (see also verse Colossians 1:18).