John Calvin Commentary Psalms 106:21

"They forgat God their Saviour, Who had done great things in Egypt," — Psalms 106:21 (ASV)

They forgot God. The prophet again repeats that the people had sinned not simply through ignorance, but also willfully, since God had already given a very clear manifestation of His power and glory. And since He makes Himself known in the creation of the heavens and the earth, human blindness is totally inexcusable.

But the sin of the children of Israel is far more aggravating. After God had made Himself known to them in the most gracious manner, they cast Him off altogether and gave themselves up to the practice of crude idolatry. And since God from heaven displayed His almighty power for their salvation, great importance must surely be attached to such displays of His power, which proclaim the praise and honor of His great name.

If He had merely given an ordinary sign of His power, even that should have commanded enough attention to keep the people in the fear and worship of God. Now, since these miracles were so very remarkable, or rather, awe-inspiring and rare, the people acted despicably by shutting their eyes to them and giving themselves over to idolatry. For just as darkness is dispelled by the radiant light of the sun, so all human contrivances and corrupt errors should vanish before such knowledge of God.