For if God has not spared the natural branches, etc. This is a most powerful reason to beat down all self-confidence: for the rejection of the Jews should never come across our minds without striking and shaking us with dread. For what ruined them, but that through supine dependence on the dignity which they had obtained, they despised what God had appointed? They were not spared, though they were natural branches; what then shall be done to us, who are the wild olive and aliens, if we become beyond measure arrogant? But this thought, as it leads us to distrust ourselves, so it tends to make us to cleave more firmly and steadfastly to the goodness of God. And here again it appears more evident, that the discourse is addressed generally to the body of the Gentiles, for the excision, of which he speaks, could not apply to individuals, whose election is unchangeable, based on the eternal purpose of God. Paul therefore declares to the Gentiles, that if they exulted over the Jews, a reward for their pride would be prepared for them; for God will again reconcile to himself the first people whom he has divorced.

For if God - If God did not refrain from rejecting the Jews who became unbelievers, assuredly he will not refrain from rejecting you in the same circumstances. It may be supposed that he will be quite as ready to reject the ingrafted branches, as to cast off those which belonged to the parent stock. The situation of the Gentiles is not such as to give them any security over the condition of the rejected Jew.

For if God spared not the natural branches - If He, in his infinite justice and holiness, could not tolerate sin in the people whom he foreknew, whom he had so long loved, cherished, miraculously preserved and blessed; take heed lest he also spare not thee. Be convinced that the same righteous principle in him will cause him to act towards you as he has acted towards them, if you sin after the similitude of their transgression; and to this, self-sufficiency and self-confidence will soon lead you. Remember, therefore, the rock whence you were hewn, and the hole of the pit whence ye were digged. Depend incessantly on God's free grace, that ye may abide in his favor.

For if God spared not the (u) natural branches, [take heed] lest he also spare not thee.
(u) He calls them natural, not because they had any holiness by nature, but because they were born of those whom the Lord set apart for himself from other nations, by his league and covenant which he freely made with them.

For if God spared not the natural branches,.... That is, executed his righteous judgments, inflicted due punishment upon the Jews, unchurched them, and stripped them of those privileges they enjoyed in a church state; who were the natural descendants of Abraham; were naturally, and as born into the world, in a national church state and in that national covenant God made with that people; to whom belonged a national adoption, in which sense they were the sons of God, his firstborn; they were chosen by him as a special and peculiar people, to very great favours and privileges; they were Christ's own, he came of them according to the flesh, and was particularly sent unto them, and ministered among them; wherefore, if, at last, God did not spare this people, though he had for a long time done it, but stirred up all his wrath against them, they disbelieving his Son, rejecting and despising the Messiah, and salvation by him, this should awaken the fear, care, and caution of the Gentiles in a church state, lest if they behave not well, he should deal in like manner with them:
take heed lest he also spare not thee; for whatever was done to the Jews in former or latter times, are written for the instruction and admonition of Gentiles; and the use they are to make thereof is, to be careful and cautious, lest by imbibing principles derogatory from the grace of God and glory of Christ, or by an unbecoming walk and conversation they provoke the Lord to unchurch them as he has done the Jews before them; and which they may the rather fear, since the Jews were the natural branches, and they formerly strangers and aliens.

For if God spared not the natural branches--sprung from the parent stem.
take heed lest he also spare not thee--a mere wild graft. The former might, beforehand, have been thought very improbable; but, after that, no one can wonder at the latter.

Be not highminded, but fear - We may observe, this fear is not opposed to trust, but to pride and security.