2 Hear the Apostle distinguishing each season, and do thou also distinguish it....“Do you think,” he says, “O man, that judgest them that do such things, and doest the same, that you shall escape the judgment of God?” And as if we were to reply, Why do I commit such sins daily, and no evil occurs unto me? He goes on to show to him the season of mercy: “Despisest thou the riches of His goodness, and forbearance, and long-suffering?” And he did indeed despise them; but the Apostle has made him anxious.
“Not knowing,” he says, “that the goodness of God leads you to repentance?” Behold the season of mercy. But that he might not think this would last for ever, how did he in the next verse raise his fears? Now hear the season of judgment; you have heard the season of mercy, on which account, “mercy and judgment will I sing unto You, O Lord:” “But you,” says the Apostle, “after your hardness and impenitent heart, treasurest up unto yourself wrath against the day of wrath, and revelation of the righteous judgment of God, who will render to every man according to his deeds.” Lo, “mercy and judgment.”
But he has threatened concerning judgment: is therefore the judgment of God to be feared only, and not to be loved? To be feared by the wicked on account of punishment, to be loved by the good on account of the crown. Because then the Apostle has alarmed the wicked in the testimony which I have quoted, hear where he gives hope concerning judgment to the good. He puts forth himself, and shows in himself too the season of mercy. For unless he found a period of mercy, in what condition would judgment find him?
A blasphemer, a persecutor, an injurer of others. For he thus speaks, and praises the season of mercy, in which season we are now living: “I who was before,” he says, “a blasphemer, and a persecutor, and injurious: but I obtained mercy.” But perhaps he only has obtained mercy? Hear how he cheers us: “That in me,” he says, “first, Christ Jesus might show forth all long-suffering, for a pattern to them which should hereafter believe in Him to life everlasting.” What means, “that He might show forth all long-suffering”?
That every sinner and wicked man might see that Paul received pardon, and might not despair of himself? Lo, he has instanced himself, and thereby cheered others also....But did Paul alone deserve this? For I had asserted, that as he raised our fears by the former testimony, so did he encourage us by the latter. When he said, “The Lord, the righteous Judge, shall render to me at that day:” he adds, “and not to me only, but unto all them also that love His appearing” and His kingdom. Since therefore, brethren, we have a season of mercy, let us not on that account flatter, or indulge ourselves, saying, God spares ever....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)