St. Ambrose’ version differs in expression from the Vulg.—Ego enim Dominus et non mutor (Mal. iii. 6)—but not in substance, for Ego sum Dominus and “I am the Lord” both mean “I am He who is”—(ὁ ὢν)—which is very well represented by Ego sum, Ego sum—“I am, I am.”—Cf. Ex. iii. 14.