…bringing the people of God to consistent Christian living in the light of the gospel of the crucified Messiah is so important to Paul that he will not turn from this goal. If he moves people in this direction by encouragement and admonition, all to the good; if severer discipline is called for, he will not flinch. So Paul offers the Corinthians a choice: “What do you prefer? Shall I come to you with a whip, or in love and with a gentle spirit?” (4:21). He does not mean, of course, that if he comes with a whip (literally, a “rod” of correction, continuing the father/son metaphor) he will not love them. The contrast refers to the manner or form of his coming, not his motives. But spankings still hurt, even from a father who insists that he is spanking his son because he loves him. It is much better for the son to change his behavior, so that the manner of the father’s coming will be not with discipline but with a gentle spirit.
In short, Christian leaders dare not overlook their responsibility to lead the people of God in living that is in conformity with the gospel. That is why Paul urges people to live a life worthy of the calling they have received (Eph. 4:1). It is why Paul prays that believers may live a life worthy of the Lord, the crucified Messiah, and may please him in every way (Col. 1:10). And if the people of God dig in their heels in disobedience, there may come a time for Christian leaders to admonish, to rebuke, and ultimately to discipline firmly those who take the name of Christ but do not care to follow him. The sterner steps must never be taken hastily or lightly. But sometimes they must be taken. That is part of the responsibility of Christian leadership.
D.A. Carson, Cross and Christian Ministry, The: Leadership Lessons from 1 Corinthians