Omit who. Now is temporal: in the midst of my imprisonment and sufferings, after having become a minister of the Gospel, and having preached it.
In my sufferings
Not as our idiom, rejoice in, as rejoice in the Lord, but in the midst of; while enduring.
Fill up (ἀνταναπληρῶ)
Only here in the New Testament. Lit., fill up in turn. Rev., on my part (ἀντί) Ἁναπληρόω to fill up occurs 1Co 14:16; 1Co 16:17; Gal 6:2, and elsewhere. The double compound προσαναπληρόω to fill up by adding, 2Co 9:12 (note); 2Co 11:9. Ἁντί on my part offsets Christ in the next clause. Lightfoot explains well: “It signifies that the supply comes from an opposite quarter to the deficiency, and so describes the correspondence of the personal agents,” and not merely the correspondence of the supply with the deficiency.
That which is lacking of the afflictions of Christ (τὰ ὑστερήματα τῶν θλίψεων τοῦ Χριστοῦ)
Lacking, lit., behind. Used with different compounds of πληρόω to fill, 1Co 16:17; 2Co 9:12; 2Co 11:9; Phi 2:30. Of the afflictions of Christ. The afflictions which Christ endured; which belonged to Him: not Paul's afflictions described as Christ's because endured in fellowship with Him (Meyer); nor the afflictions which Christ endures in His Church (Alford, Ellicott, Eadie).
These afflictions do not include Christ's vicarious sufferings, which are never denoted by θλίψεις tribulations. That which is lacking of the afflictions of Christ signifies that portion of Christ's ministerial sufferings which was not endured by Him in person, but is endured in the suffering of Christians in all generations in carrying out Christ's work. Compare 2Co 1:5, 2Co 1:7; Phi 3:10. Hence those are mistaken interpretations which explain the filling up as a correspondence of the supply with the deficiency. The correspondence is between the two parties, Christ and His followers, and the supply does not correspond with the deficiency, but works toward supplying it. The point is not the identification of Paul with Christ in His sufferings (which is true as a fact), but the distinction between Paul and Christ. Hence the present tense, I am filling up, denoting something still in process. The full tale of sufferings will not be completed until the Church shall have finished her conflict, and shall have come up “out of great tribulation” to sit at the marriage-supper of the Lamb.
In my flesh
Connect with fill up.
For His body's sake, which is the Church
Σάρξ flesh is never used of a metaphorical organism like the Church, but σῶμα body. See on flesh, Rom 7:5, sec. 3. In Col 1:22, flesh was used with body in order to define the reference of body to the fleshly human organism of Christ. Compare Joh 1:14. Here σῶμα body only, defined by Church.