Rom 11:21

“For if these men of old time, who preceded us in the gifts [bestowed upon them], and for whom the Son of God had not yet suffered, when they committed any sin and served fleshly lusts, were rendered objects of such disgrace, what shall the men of the present day suffer, who have despised the Lord's coming, and become the slaves of their own lusts? And truly the death of the Lord became [the means of] healing and remission of sins to the former, but Christ shall not die again in behalf of those who now commit sin, for death shall no more have dominion over Him; but the Son shall come in the glory of the Father, requiring from His stewards and dispensers the money which He had entrusted to them, with usury; and from those to whom He had given most shall He demand most. 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."”

“The reason for this admonition is given when he says: for if God has not spared the natural branches, i.e., the Jews, who descended by natural origin from the patriarchs, but allowed them to be broken off, fear lest perhaps also he does not spare you, i.e., lest he permit you to be broken off because of unbelief: the jealously and rage of the husband will not spare on the day of revenge (Prov 6:34); I will not spare and I will not pardon; nor will I have mercy, but to destroy them (Jer 13:14). This, therefore, is the Apostle's answer; that when someone sees that he has obtained grace and another has fallen, he should not boast against the fallen but rather fear for himself, because pride is the cause of falling headlong and fear is the cause of carefulness and being kept safe.”