Matthew Henry Commentary Deuteronomy 32:15-18

"But Jeshurun waxed fat, and kicked: Thou art waxed fat, thou art grown thick, thou art become sleek; Then he forsook God who made him, And lightly esteemed the Rock of his salvation. They moved him to jealousy with strange [gods]; With abominations provoked they him to anger. They sacrificed unto demons, [which were] no God, To gods that they knew not, To new [gods] that came up of late, Which your fathers dreaded not. Of the Rock that begat thee thou art unmindful, And hast forgotten God that gave thee birth." — Deuteronomy 32:15-18 (ASV)

Here are two instances of the wickedness of Israel, each an apostasy from God. These people were called Jeshurun—interpreted by some as “an upright people,” and by others as “a seeing people”—but they soon lost their reputation for both knowledge and righteousness.

They indulged their appetites, as if they had nothing to do but to make provision for the flesh to fulfill the lusts of it. Those who make a god of themselves and a god of their bellies, in pride and wantonness, and cannot bear to be told of it, thereby forsake God and show they esteem him lightly.

There is only one way for a sinner's acceptance and sanctification, even though different forms of irreligion or false religion may show a favorable regard for other paths—a regard often miscalled 'candid.' How mad are idolaters, who forsake the Rock of salvation, only to run themselves upon the rock of perdition!