1 Corinthians 9:19
For though I be free from all [men], yet have I made myself servant unto all, that I might gain the more.
Note 6 at 1Co 9:19: Paul didn't serve man; therefore, no man could dictate to him. Yet he loved everyone and had therefore voluntarily made himself a servant to others. We should not be servants out of fear, but as true Christians, we should be indebted to everyone (Ro 1:14) because of the love of Christ (2Co 5:14).
Remember that, in context, Paul was saying these things to illustrate to those who knew they were free to eat meat sacrificed to idols, that he had voluntarily laid aside many of his rights for the good of others (see note 1 at 1Co 9:1). If the Apostle Paul--who was greater in authority and in every spiritual qualification than those he was writing to--had humbled himself and placed the needs of others ahead of his own, then how could they do less?