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....
3. “I will sing to the harp, and will have understanding, in the spotless way. When You shall come unto me”. Except in the spotless way, you can neither sing to the harp, nor understand. If you dost wish to understand, sing in the spotless way, that is, work with cheerfulness before your God. What is the spotless way? Hear what follows: “I walked in innocence, in the midst of my house.” This spotless way begins from innocence, and it ends also in innocence. Why seek many words? Be innocent: and you have perfected righteousness....But who is innocent? He who while he hurts not another, injures not himself. For he who hurts himself, is not innocent. Some one says: Lo, I have not robbed any one, I have not oppressed any one: I will live happily on my own substance, the fruits of my virtuous toil; I wish to have fine banquets, I wish to spend as much as pleases me, to drink with those whom I like as much as I please; whom have I robbed, whom have I oppressed, who has complained of me? He seems innocent. But if he corrupt himself, if he overthrow the temple of God within himself, why hope that he will act with mercy toward others, and spare the wretched? Can that man be merciful to others, who unto himself is cruel? The whole of righteousness, therefore, is reduced to the one word, innocence. But the lover of iniquity, hates his own soul. When he loved iniquity, he fancied he was injuring others. But consider whether he was injuring others: “He who loves iniquity,” he says, “hates his own soul.” He therefore who wishes to injure another, first injures himself; nor does he walk, since there is no room. For all wickedness suffers from narrowness: innocence alone is broad enough to walk in. “I walked in the innocence of my heart, in the midst of my house.” By the middle of his house, he either signifies the Church herself; for Christ walks in her: or his own heart; for our inner house is our heart: as he has explained in the above words, “in the innocence of my heart.” What is the innocence of the heart? The middle of his house? Whoever has a bad house in this, is driven out of doors. For whoever is oppressed within his heart by a bad conscience, just as any man in consequence of the overflow of a waterspout or of smoke goes out of his house, suffers not himself to dwell therein; so he who has not a quiet heart, cannot happily dwell in his heart. Such men go out of themselves in the bent of their mind, and delight themselves with things without, that affect the body; they seek repose in trifles, in spectacles, in luxuries, in all evils. Wherefore do they wish themselves well without? Because it is not well with them within, so that they may rejoice in a good conscience....
4. “I set no wicked thing before my eyes”....I did love no wicked thing. And he explains this same wicked thing: “I hated them that do unfaithfulness.” Attend, my brethren. If you walk with Christ in the midst of His house, that is, if either in your heart you have a good repose, or in the Church herself proceed on a good journey in the way of godliness; ye ought not to hate those unfaithful only who are without, but whomsoever also ye may have found within. Who are the unfaithful? They who hate the law of God; who hear, and do it not, are called unfaithful. Hate the doers of unfaithfulness, repel them from you. But you should hate the unfaithful, not men: one man who is unfaithful, has, you see, two names, man, and unfaithful: God made him man, he made himself unfaithful; love in him what God made, persecute in him what he made himself. For when you shall have persecuted his unfaithfulness, you kill the work of man, and freest the work of God. “I hated the doers of unfaithfulness.”
5. “The wicked heart has not cleaved unto me.”...The heart of a man, who wishes not anything contrary to any that God wishes, is called straight....If therefore the righteous heart follows God, the crooked heart resists God. Suppose something untoward happens to him, he cries out, “God, what have I done unto You? What sin have I committed?” He wishes himself to appear just, God unjust. What is so crooked as this? It is not enough that you are crooked yourself: you must think your rule crooked also. Reform yourself, and you find Him straight, in departing from whom you have made yourself crooked. He does justly, thou unjustly; and for this reason you are perverse, since you call man just, and God unjust. What man do you call just? Yourself. For when you say, “What have I done unto You?” you think yourself just. But let God answer you: “You speak truth: you have done nothing to Me: you have done all things unto yourself; for if you had done anything for Me, you would have done good. For whatever is done well, is done unto Me; because it is done according to My commandment; but whatever of evil is done, is done unto you, not unto Me; for the wicked man does nothing except for his own sake, since it is not what I command.” When ye see such men, brethren, reprove them, convince and correct them: and if you cannot reprove or correct them, consent not to them.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)