Isaiah 43:18 (ESV) … “Remember not the former things, nor consider the things of old.”
Great indeed was the deliverance at the time of the exodus. Nevertheless, this was but a foretaste of a deliverance far greater. Therefore, the people are not to remember the exodus and to consider it as the full object of their attention. Not that they are to give no thought at all to what God has already done, but what He is about to do is so much greater that they should turn all their thought to what is yet to come.
The prophet strengthens his command by the chiastic arrangement of the verse: imperative, object; object, imperative. First things and former things are really synonyms and refer to the things that took place long ago when the people were first formed into a nation. The negatives are not expressed by lô’, as though to give a strict prohibition, but by the milder ’al; hence, Ye should not remember, etc. Thus the prophet prepares the people’s hearts and minds for a consideration of the wondrous deliverance to come. To this new thing their entire undivided attention and thought must be given.
We also must consider the great things yet to come. While our deliverance at Calvary is always a paramount moment of remembrance, we also live with an eye on our Heavenly deliverance yet to come.
 Young, E. (1972). The Book of Isaiah, Chapters 40–66 (Vol. 3, p. 155). Grand Rapids, MI: Wm. B. Eerdmans Publishing Co.