Deuteronomy 32:21

They have moved me to jealousy with [that which is] not God,
&c.] With a false messiah; for after the death of Jesus, the true Messiah, God as well as man, many false Christs arose, as he predicted, and were received for a time, who were mere men, and deceivers; and their now vainly expected messiah, or whom they look for, according to their own sense of him, is no other than a mere creature, and not God: or with the idol of their own righteousness; which, as an idol is nothing in the world, that is, nothing in the business of justification, and put in the room of Christ highly provokes the Lord to jealousy:

they have provoked me to anger with their vanities;
such were their false Christs they in vain trusted in, and such the idol of their own righteousness they set up, but could not make to stand; and such were the traditions of their elders; they put upon an equality with, or above the word of God; all which stirred up the wrath and anger of God against them:

and I will move them to jealousy with [those which are] not a people:
this is not to be understood of any particular nation, but of the Gentiles in general, and of God's elect among them, and of the calling of them; which would be provoking to the Jews, as the Apostle Paul has taught us to understand it, ( Romans 10:19 ) . These were not the people of God, or not my people, as he says ( Romans 9:25 Romans 9:26 ) ( 1 Peter 2:10 ) ; In some sense indeed they were his people, being chosen by him, and taken into covenant with him; for he is God not of the Jews only, but of the Gentiles also; and those were given to Christ as his people, and are his other sheep which were not of the Jewish fold; and who were redeemed by him to be a peculiar people out of every kindred, tongue, people, and nation, all which was before their calling: yet, in another sense they were not his people; they were without any spiritual privileges, the word and ordinances, without the knowledge of God and Christ, without communion with them; they were not a people near unto the Lord, he had not laid hold on and formed them for himself in regeneration and conversion; they were not reckoned the people of God, nor called so, and especially by the Jews, who accounted themselves to be the only people of God; see ( Ephesians 2:11 Ephesians 2:12 ) ;

I will provoke them to anger with a foolish nation;
either the Romans in particular are meant, so called because of their gross idolatry, to which they were addicted, who otherwise in their political affairs were a wise and understanding people; to these Judea became a province, and were subject to tribute; and by the exactions of the Romans, and their ill usage of them, they were provoked to rise against them, which issued in their ruin: or rather the Gentiles in general, who might be called foolish because of their superstition and idolatry, ignorance, and blindness in religious matters, and especially were so in the account of the Jews; and the elect of God among them in particular, who in their state of unregeneracy were foolish, as all unregenerate men are; both their principles and practices were foolish, and they were the foolish things of the Gentile world that God chose and called: and the calling of them was exceedingly provoking to the Jews; which was as if a man, moved to jealousy by the behaviour of his wife, should strip her of her ornaments and jewels, and reject her as his wife; and take another before her eyes of mean estate, and marry her, and put her ornaments on her, to which the allusion is; for the Lord, being moved to jealousy by the conduct of the Jewish nation towards him, rejected them from being his people, and stripped them of all their privileges, civil and religious, and took the Gentiles in the room of them, and so in just retaliation moved them to jealousy and wrath. It was displeasing to the carnal Jews to hear of the prophecies of the calling of the Gentiles, ( Romans 10:20 ) ; and the first display of grace to them was resented even by believing Jews themselves at first, ( Acts 11:2 Acts 11:3 Acts 11:18 ) . The anger of the Scribes and Pharisees on this account is thought by some to be hinted at in the parable of the two sons, ( Luke 15:27 Luke 15:28 ) . The Jews were offended with Christ for eating with publicans, the Roman tax gatherers, and were greatly displeased when he told them the kingdom of God would be taken from them, and given to another nation, ( Matthew 9:10 Matthew 9:11 ) ( Matthew 21:43 Matthew 21:46 ) . Their rage and envy were very great when the Gospel was first preached to the Gentiles, ( Acts 13:41 Acts 13:44-46 ) ; and there is such an extraordinary instance of their spite and malice to the Gentiles, and of their jealousy and anger they were moved unto, as is not to be paralleled, ( 1 Thessalonians 2:15 1 Thessalonians 2:16 ) .