These words are not an exaggeration. The reason they are not true of us who call ourselves ministers of the gospel is not that Paul forgot the exact truth in using them, but that we have too many discreet affinities to allow ourselves to be made refuse. "Filling up that which is behind of the afflictions of Christ" is not an evidence of sanctification, but of being "separated unto the gospel."
"Think it not strange concerning the fiery trial which is to try you," says Peter. If we do think it strange concerning the things we meet with, it is because we are craven-hearted. We have discreet affinities that keep us out of the mire – I won’t stoop, I won’t bend. You do not need to, you can be saved by the skin of your teeth if you like; you can refuse to let God count you as one separated unto the gospel. Or you may say – "I do not care if I am treated as the offscouring of the earth as long as the Gospel is proclaimed." A servant of Jesus Christ is one who is willing to go to martyrdom for the reality of the gospel of God. When a merely moral man or woman comes in contact with baseness and immorality and treachery, the recoil is so desperately offensive to human goodness that the heart shuts up in despair. The marvel of the Redemptive Reality of God is that the worst and the vilest can never get to the bottom of His love. Paul did not say that God separated him to show what a wonderful man He could make of him, but "to reveal His Son in me."