Ye are my witnesses - They were his witnesses, because, first, he had given in them predictions of future events which had been literally fulfilled: secondly, by his power of delivering them so often manifested, he had shown that he was a God able to save. Neither of these had been done by the idol-gods (compare Isaiah 44:8).
And believe me - Or rather, confide in me.
Before me there was no God formed - I am the only true, the eternal God. In this expression, Yahweh says that he was the first being. He derived his existence from no one. Perhaps the Hebrew will bear a little more emphasis than is conveyed by our translation. ‘Before me, God was not formed,’ implying that he was God, and that he existed anterior to all other beings. It was an opinion among the Greeks, that the same gods had not always reigned, but that the more ancient divinities had been expelled by the more modern. It is possible that some such opinion may have prevailed in the oriental idolatry, and that God here means to say, in opposition to that, that he had not succeeded any other God in his kingdom. His dominion was original, underived, and independent.
Neither shall there be after me - He would never cease to live; he would never vacate his throne for another. This expression is equivalent to that which occurs in the Book of Revelation, ‘I am Alpha and Omega, the first and the last’ Revelation 1:11; and it is remarkable that this language, which obviously implies eternity, and which in Isaiah is used expressly to prove the divinity of Yahweh, is, in the passage referred to in the Book of Revelation, applied no less unequivocally to the Lord Jesus Christ.