Colossians 1:24
24Now I rejoice in my sufferings for your sake, and fill up on my part that which is lacking of the afflictions of Christ in my flesh for his body’s sake, which is the assembly,
Paul rejoices in sufferings for the Colossians’ sake—not grim endurance but glad participation. What is lacking is not a deficit in the cross’s atoning value; Christ’s once-for-all sacrifice is complete. The lack is the still-unfolding afflictions His body bears as the gospel advances.
Those in Wesley’s line hear a willing steward: grace enables Paul to offer his flesh for the church without adding to Calvary. We may likewise choose, under assisting grace, to suffer for others’ good while resting wholly in Christ’s finished work.
Joy in affliction is not stoicism; it is union with Christ for the church’s sake. Reformed readers insist with Paul that nothing is lacking in the atonement—the “lack” is the remaining share of Messianic sufferings appointed for the body until the mission is done.
Christ’s afflictions continue in His members under the Father’s providence. Paul’s flesh fills what the Head still assigns to His body; the cross remains sufficient, and the church is served by sufferings God orders for her good.