Albert Barnes Commentary Isaiah 54:9

"For this is [as] the waters of Noah unto me; for as I have sworn that the waters of Noah shall no more go over the earth, so have I sworn that I will not be wroth with thee, nor rebuke thee." — Isaiah 54:9 (ASV)

For this is as the waters of Noah to me — As it was in the time of the flood of waters, so shall it be now. ‘I then solemnly promised that the waters should not again drown the earth, and I have kept that promise. I now promise with equal solemnity that I will bestow perpetual favor on my true people, and will shed upon them eternal and unchanging blessings.’

‘The waters of Noah,’ here mean evidently the flood that came upon the world in his time, and from which he and his family were saved. Lowth, on the authority of one manuscript and of the Vulgate, Syriac, Symmachus, and Theodotion, reads this: ‘In the days of Noah.’ But the authority is not sufficient to change the Hebrew text, and the sense is as clear as if it were changed.

As I have sworn — (Genesis 8:21–22). God appeals to this not only because the oath and promise had been made, but because it had been kept.

That I would not be wroth — The idea here seems to be that no calamities should spread over the whole church and sweep it away, as the waters swept over the world in the time of Noah, or as desolation swept over Jerusalem and the whole land of Canaan in the time of the exile at Babylon. There would indeed be persecutions and calamities, but the church would be safe amid all these trials. The period would never arrive when God would forsake the church, and when he would leave it to perish.

One has only to recollect how God has guarded the church, even during the most dangerous periods, to see how remarkably this has been fulfilled. His covenant has been as sure as that which was made with Noah, and it will be as secure and firm to the end of time.