to compel: to bring pressure on someone so that they act, whether by force, by authority, or by sheer insistence
This verb is about pressure put on a person. Someone or something bears down on them until they act, and the act is not the free choice they would have made on their own. The related noun names the necessity itself (ἀνάγκη); this is the verb for laying that necessity on somebody.
How hard the pressure pushes is not in the word. It is in the situation, and in the New Testament the situations lie a long way apart:
- Jesus presses his disciples into a boat and sends them on ahead of him.
- A servant is sent out to press strangers off the roads into a banquet hall.
- Paul, before he believed, punishes Christians in the synagogues to make them curse Christ.
- Teachers in Galatia push Gentile converts into circumcision to keep themselves out of trouble.
The same verb covers a friend who will not take no and a persecutor with the power to punish. Only the sentence around it tells you which.
The word also works the other way round, with nobody doing the pushing. When Paul appeals to Caesar, the accusations against him have closed off every other road; when he tells the Corinthians they forced him into boasting, he means their silence left him no other move. Nobody here is being bullied. A situation has simply run out of alternatives.
What holds all of this together is the loss of a free choice. That is why the word becomes an accusation in Galatians: to pressure fellow Christians in a matter of conscience is to take back the freedom they were given, so Paul treats it as an attack on the good news itself and not a lapse in manners.