Deuteronomy 29:25

Then men shall say
The answer that will be returned to the above questions will be this

because they have forsaken the covenant of the Lord God of their
fathers:
breakers of covenants with men are always reckoned among the worst of men, see ( Romans 1:31 ) ; and especially breakers of covenant with God, and with such a God as the God of Israel was, so good, so kind, and gracious; and of such a covenant he made with them, in which so many good things were promised unto them, on condition of their obedience; as the continuance in, such a land they dwelt in, with an abundance of privileges, civil and religious: and this covenant God of theirs was the God of their fathers also; and it was always reckoned an heinous sin among the Heathens to forsake the gods of their ancestors; see ( Jeremiah 2:11 ) ;

which he made with them when he brought them out of the land of Egypt;
which is another aggravation of their breach of the covenant the Lord made with them; it being made with them by that God, and at that time, when he in so wonderful a manner, with such mighty power, and a outstretched arm, and in great kindness and tenderness to them, brought then, out of hard bondage and most wretched slavery in Egypt.