And do you wish that I should speak of another instance of God's goodness? It is not only this, but that He does not suffer the good to become bad. For if they were destined to meet with the same things, they would all be bad. But now this also does not a little console the good. For hear the Prophet, saying, “The righteous shall rejoice when he sees the vengeance upon the ungodly, he shall wash his hands in the blood of the sinner.” Not rejoicing on account of it, God forbid!
But fearing lest he should suffer the same things, he will render his own life more pure. This then is a mark of His great care. Yes, you say, but He ought only to threaten, and not to punish also. But if He does punish, and still you say it is a matter of threat, and on that account become more slothful, if it were really but a threat, would you not become more supine? If the Ninevites had known it was a matter of threat, they would not have repented. But because they repented, they cause the threat to stop at words only.
Do you wish it to be a threat only? You have the disposal of that matter. Become a better man, and it stops only at the threat. But if, which be far from you! Thou despises the threat, you will come to the experience of it. The men before the flood, if they had feared the threat, would not have experienced the execution of it. And we, if we fear the threat, shall not expose ourselves to experience the reality. God forbid we should. And may the merciful God grant that we all henceforth, having been brought to sound mind, may obtain those unspeakable blessings. Of which may we all be thought worthy, through the grace and lovingkindness of our Lord Jesus Christ, with whom to the Father, together with the Holy Ghost, be glory, power, and honor, now and for ever and ever. Amen.
Source: Homilies on Philemon (New Advent)