" While Jesus does not directly charge his followers with fighting human foes (though there have been those who have found an implicit justification for such in the name of a righteous cause), many of the faith’s adherents have seen the gospel as a call to continue Christ’s cause by engaging in another kind of warfare — one waged on the spiritual plane. The Bible is full of references both to contest — what the ancient Greeks called agon — and to war. Individuals wrestle with God (both metaphorically and literally), and the apostle Paul refers to believers as “athletes” who must “train” their souls and run the race set before them. Believers are to gird themselves about with spiritual “armor,” and wield the “sword of the spirit” in battling unseen forces and directly confronting the conflict between good and evil. "
― Brett McKay , Muscular Christianity: The Relationship Between Men and Faith