Deuteronomy 32:15

But Jeshurun waxed fat, and kicked
This is undoubtedly a name of the people of Israel; it is to be met with only in three places more, in ( Deuteronomy 33:5 Deuteronomy 33:26 ) ( Isaiah 44:2 ) ; it is generally thought to come from a word ^F4 which signifies upright and righteous, such these people ought to have been, and some among them were; and they generally professed themselves, and outwardly appeared to be upright, just, and righteous persons, and were desirous of being reckoned so; which was their character in the times of Christ, when they rejected him: others derive it from a word ^F5 which signifies to behold, to see, and so describes them as seeing ones; and such they had been in the times of Moses, saw extraordinary sights and wonders in Egypt, the great salvation at the Red sea, the Lord going before them in a pillar of cloud and life; the manna every day falling about their tents; twice rocks smitten, and waters flowing from them, and had often very uncommon sights of the glory of God: and in the times of Christ, to which this song refers, they saw him in the flesh, preaching in their synagogues, doing miracles, riding on an ass to Jerusalem, according to one of their prophecies, and expiring on the cross, and yet rejected him. They are said to "wax fat", enjoy great outward prosperity, to abound in temporal good things, as they also did in spiritual, privileges; enjoying, or they might have enjoyed, such a ministry of the word, as never was before or since, the ministry of John the Baptist, the forerunner of Christ, of Christ himself, and of his apostles, yet they "kicked"; which may denote their disobedience to the laws of God, moral and ceremonial, see ( 1 Samuel 2:29 ) ( Nehemiah 9:25 Nehemiah 9:26 ) ; and particularly the introduction of idolatry among them, which was kicking against God, and his worship; first among the ten tribes, in the times of Jeroboam, and among the two tribes, more especially in the times of Manasseh; and this kicking was particularly verified in Judas's lifting up his heel against Christ, and betraying him; which was not merely the sin of him only, but what the whole body of the people were involved in, see ( Psalms 41:9 ) ( Acts 7:52 ) :

thou art waxen fat, thou art grown thick, thou art covered [with
fatness];
which is repeated and expressed by different words, both for the certainty of it, and to denote their great affluence of good things, and so the more to aggravate their impiety and ingratitude, next observed:

then he forsook God [which] made him;
the worship of God, as the Targum of Jonathan, giving into idolatry in times past; and the written word of God, by giving heed to the traditions of the elders, to the making void and of none effect the word of God; or Christ, the essential Word of God; so the Targum of Jonathan,

``and left the Word of God, who created them;''

and lightly esteemed the rock of his salvation;
the same divine Person, described in ( Deuteronomy 32:4 ) ; and there called "the Rock", (See Gill on Deuteronomy 32:4); here "the rock of salvation"; because salvation flows from him: he is the author of it, and it is to be had of him, and no other; and this epithet shows not only his ability and strength to effect it, but the security of it in him, which being wrought out is an everlasting one. He is said to be the rock of "his" salvation, Jeshurun or Israel, he being of the Jews, raised up among them, and sent unto them, and was the Saviour of some of them actually, even of the lost sheep of the house of Israel, and on account of his salvation deserving of universal esteem. But the Jews "lightly esteemed" him, had no value for him, set this rock and stone at nought; he was refused and rejected by the builders, who is now the head of the corner; they despised him, mocked at him, and treated him with the utmost contempt and disdain, yea, with abhorrence; all which, and more, is signified by the word here used: they traduced him as a vile and wicked person, and charged and, treated him as such, so some render the word ^F6; and, as others ^F7, they made a dead carcass of him, they crucified and slew him; this is the crime of ingratitude hinted at in ( Deuteronomy 32:6 ) ; and all between is an enumeration of instances of divine goodness to this people, mentioned with a view to aggravate this unheard of sin.