We ought not, therefore, as that presbyter remarks, to be puffed up, nor be severe upon those of old time, but ought ourselves to fear, lest perchance, after we have come to the knowledge of Christ, if we do things displeasing to God, we obtain no further forgiveness of sins, but be shut out from His kingdom. And therefore it was that Paul said, "For if God spared not the natural branches, take heed lest He also spare not thee, who, when thou wert a wild olive tree, wert grafted into the fatness of the olive tree, and wert made a partaker of its fatness."
"For if God spared not the natural branches," and then he does not say, neither will He spare thee," but "take heed, lest He also spare not thee." So paring away the distasteful from his statement, representing the believer as in the struggle, he at once draws the others to him, and humbles these also.
[AD 202] Irenaeus on Romans 11:21