1 Samuel 29:6 - Coke's Commentary on the Holy Bible

Surely, as the Lord liveth— It is observable, that Achish on this occasion makes use of that form of swearing which obtained among the Jews, as the Lord liveth; from which some have concluded, that Achish had learned a part of David's religion; and others go into great extremes on the other side; for which, I own, I can see no grounds. David was a man of sufficient address; he well knew how to converse with kings; nor was Achish the first whose favour his accomplishments had acquired him. In all probability, he stipulated for the free exercise of his religion, before he threw himself into his service; and such a stipulation might naturally be attended with an apology in its favour. Nor will David's character suffer us to suppose him so cold and unconcerned in that point, as to omit any opportunity of recommending his religion to the best advantage; for surely no mortal ever had it more at heart; especially after that declaration, which he himself has made in the 119th Psalm, sect. 6. (vau) I will speak of thy testimonies even before kings, and will not be ashamed. What wonder then if David should have instructed, and Achish profited in this point from David's conversation? But after all, possibly, Achish might have sworn by Jehovah on this occasion, as that Jew did by Jesus, whom the old duke of Ormond, (so properly, and with so fine a satire upon that profaneness too common among Christians,) reproved for his assurance, in presuming to swear like a Christian.