Adam Clarke on Romans 11:21

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.