This Chapter addresses the concept of sin in military chaplains’ instruction as well as courage, which was tied to avoiding sin. The Royalist clergy put a lot of effort in trying to eradicate certain infractions from the King’s armies, most prominently swearing, and achieving this moral reformation was one of their top priorities due to two reasons: to appease the Lord’s wrath and to enhance their public stature. Puritan ministers, by contrast, focused on sin mainly when the fortunes of war were against them. Military defeats were a sign of God’s disfavour whereas victories and success were an assurance that he was on their side. Hence, instead of obsessively overseeing soldiers’ moral infractions, Parliamentarian ministers emphasised active pursuit of military victories. Moreover, sins were seen as detrimental to the true Christian courage needed in the war. ‘Swearing Cavaliers’ were criticised for their heathen bravery and displays of unwanted valour, such as duelling. Right kind of religious courage was emphasised both to set own soldiers apart from the enemy and also to regulate counterproductive behaviour in armies.