Adam Clarke Bible Commentary

Therefore my people shall know - The word לכן lachen, occurring the second time in this verse, seems to be repeated by mistake. It has no force nor emphasis as a repetition; it only embarrasses the construction and the sense. It was not in the copies from which the Septuagint, Syriac, and Vulgate were translated; it was not in the copy of the Septuagint from which the Arabic was translated; but in the Aldine and Complutensian editions δια τουτο is repeated; probably so corrected, in order to make it conformable with the Hebrew text. I am he that Moth speak "I am he, Jehovah, that promised" - For הוא hu, the Bodleian MS. and another have יהוה, Jehovah; "For I am Jehovah that promised;" and another ancient MS. adds יהוה Jehovah after הוא hu. The addition of Jehovah seems to be right in consequence of what was said in the preceding line, "My people shall know my name."