How did he do that?

[W]e never see the importance of the Christian virtue of faithfulness more than we do in Paul’s long final imprisonment, and we never see more than here the way it is grounded in the faithfulness of Jesus himself. Paul never expected that he had to summon up this fidelity—this courage and trust and superhuman endurance—from his own meager fleshly resources. This had to be the gift of God, and all gifts of God ultimately come through Jesus, the great gift from God, and from their Spirit. We can be faithful ultimately only because he has been faithful, and yet because he has been faithful we can be faithful to an extraordinary degree. This is the final theological lesson we see figuring forth from Paul’s final biographical chapter.—Paul: An Apostle’s Journey, 177