They forgot God The prophet again repeats that the people had sinned not simply through ignorance, but also wilfully, inasmuch as God had already given a very palpable manifestation of his power and glory. And as he makes himself known in the creation of the heavens and of the earth, the blindness of men is totally inexcusable. But far more aggravating is the sin of the children of Israel, who, after God had made himself known to them, in the most condescending manner, cast him off altogether, and gave themselves up to the practice of brutish idolatry. And God having from heaven put forth his Almighty power for their salvation, there must surely be no little importance attached to such displays of his power as proclaim the praise and honor of his great name. Had he merely given an ordinary token of his power, even that ought to have attracted so much consideration as should have kept the people in the fear and worship of God. Now, that these miracles were so very notable, or rather terrible and rare, the people acted a very base part to shut their eyes upon them, and give themselves over to idolatry. For as the darkness is dispelled by the beamy lustre of the sun, so all inventions and perverse errors should vanish before such knowledge of God.

They forgat God their Saviour - The God who had saved, or delivered them, out of Egypt. The sentiment here is the same as in Psalm 78:11-12. See the notes at that place.

They forgat God their Saviour,.... Not only forgat the works of God, Psalm 106:13, but forgat God that did those mighty works; forgat that there was a God; or however forgat him that is the only true and living God, when they said of the molten image, "these are thy gods, O Israel"; and what aggravated their crime was, they forgot that God that had saved them in so wonderful a manner out of the hand of their enemies, for his own name's sake; and had led them safely through the Red sea as on dry land, and destroyed those that hated them.
Which had done great things in Egypt: meaning the ten plagues on the Egyptians, and the deliverance of the Israelites from them.