Why should we not swear, by heaven?

This brings us to James's admonishment in verse 12, "Above all, my brothers, do not use an oath when you make a promise." He tells us not to invoke the name of God with such sayings as, "I shall do such-and-such, by God." What he means by this is that we should not presume to know God's Will, or for that matter we should not presume impose our will upon God. This would be the height of arrogance. He ends verse 12 by saying that any man who makes such oaths will come under God's judgement.