Romans 11:18

boast not against, &c. i.e. against the branches that were broken off; as if in a better position than theirs might have been, and as if better in yourself, and so (as regards any virtue of your own) better able to hold your place. Every insulting thought, word, or act, of professing Christians towards Jews, as Jews, from that day to this, is an illustration of this verse. Too often such slights are also offered, in one form or another, to the re-ingrafted branches converted Jews.

thou bearest not, &c. i.e. Divine mercy has reached thee through Abraham and his sons, not them through thee.