Remember ye not the former things, neither consider the things of old.

Wesley's Notes

43:18 Remember not - Tho' your former deliverance out of Egypt was glorious: yet in comparison of that inestimable mercy of sending the Messiah, all your former deliverances are scarce worthy of your remembrance and consideration.

Jamieson-Fausset-Brown Bible Commentary

18. So wonderful shall be God's future interpositions in your behalf, that all past ones shall be forgotten in comparison. Plainly the future restoration of Israel is the event ultimately meant. Thus the "former things" are such events as the destruction of Sennacherib and the return from Babylon. "Things of old" are events still more ancient, the deliverance from Egypt and at the Red Sea, and entry into Canaan [Vitringa].

Matthew Henry's Concise Commentary

43:14-21 The deliverance from Babylon is foretold, but there is reference to greater events. The redemption of sinners by Christ, the conversion of the Gentiles, and the recall of the Jews, are described. All that is to be done to rescue sinners, and to bring the believer to glory, is little, compared with that wondrous work of love, the redemption of man.