It’s hard enough to deal with opposition from one’s enemies. But David was fleeing from his own son, Absalom, who had led a revolt and taken the city of Jerusalem and had himself proclaimed king.
Many of those who had once followed David had concluded that God had abandoned him, and mocked him. But David was still confident in God, at peace enough to sleep well even knowing he would soon face a large army in battle.
In Paul’s day, most Jewish teachers had no authority to teach new interpretations of Scripture but rather passed on the accepted interpretations they had themselves learned from others. Their credentials as teachers would thus be important to establish.
Paul’s opponents, who were leading the Galatian Christians astray, apparently had impressive credentials. But Paul makes it clear that his authority depends not on any of the apostles in Jerusalem or other human teachers, but that he teaches what he has received directly from God.