But this concerns the Second Commandment. For those who swear a true oath to the government honor God’s name and adorn the truth. Moreover, they remove suspicions. Accordingly, the godly do a good thing when they bear witness to the truth by means of an oath. On the other hand, the ungodly do nothing right, because they always have this label attached to themselves: “These people err in heart” (Ps. 95:10).
Luther’s works, vol. 4: Lectures on Genesis: Chapters 21-25 p 78