Mercy and Pity in the Judgment of God
This is the order observed in the psalm, where it is said: “Bless the Lord, O my soul, and forget not all His recompenses; who forgives all your iniquities; who heals all your diseases; who redeems your life from destruction; who crowns you with loving-kindness and tender mercy; who satisfies your desire with good things.” And lest by any chance these great blessings should be despaired of under the deformity of our old, that is, mortal condition, the Psalmist at once says, “Your youth shall be renewed like the eagle's;” as much as to say, All that you have heard belongs to the new man and to the new covenant.
Now let us consider together briefly these things, and with delight contemplate the praise of mercy, that is, of the grace of God. “Bless the Lord, O my soul,” he says, “and forget not all His recompenses.” Observe, he does not say blessings, but recompenses; because He recompenses evil with good. “Who forgives all your iniquities:” this is done in the sacrament of baptism. “Who heals all your diseases:” this is effected by the believer in the present life, while the flesh so lusts against the spirit, and the spirit against the flesh, that we do not the things we would; while also another law in our members wars against the law of our mind; while to will is present indeed to us but not how to perform that which is good. These are the diseases of a man's old nature which, however, if we only advance with persevering purpose, are healed by the growth of the new nature day by day, by the faith which operates through love. “Who redeems your life from destruction;” this will take place at the resurrection of the dead in the last day.
“Who crowns you with loving-kindness and tender mercy;” this shall be accomplished in the day of judgment; for when the righteous King shall sit upon His throne to render to every man according to his works, who shall then boast of having a pure heart? Or who shall glory of being clean from sin? It was therefore necessary to mention God's loving-kindness and tender mercy there, where one might expect debts to be demanded and deserts recompensed so strictly as to leave no room for mercy.
He crowns, therefore, with loving-kindness and tender mercy; but even so according to works. For he shall be separated to the right hand, to whom, it is said, “I was an hungered, and you gave me meat.” There will, however, be also “judgment without mercy;” but it will be for him “that has not showed mercy.” But “blessed are the merciful: for they shall obtain mercy” of God. Then, as soon as those on the left hand shall have gone into eternal fire, the righteous, too, shall go into everlasting life, because He says: “This is life eternal, that they may know You the only true God, and Jesus Christ whom You have sent.” And with this knowledge, this vision, this contemplation, shall the desire of their soul be satisfied; for it shall be enough for it to have this and nothing else—there being nothing more for it to desire, to aspire to, or to require.
It was with a craving after this full joy that his heart glowed who said to the Lord Christ, “Show us the Father, and it suffices us;” and to whom the answer was returned, “He that has seen me has seen the Father.” Because He is Himself the eternal life, in order that men may know the one true God, You and whom You have sent, Jesus Christ. If, however, he that has seen the Son has also seen the Father, then assuredly he who sees the Father and the Son sees also the Holy Spirit of the Father and the Son.
So we do not take away free will, while our soul blesses the Lord and forgets not all His recompenses; nor does it, in ignorance of God's righteousness, wish to set up one of its own; but it believes in Him who justifies the ungodly, and until it arrives at sight, it lives by faith—even the faith which works by love. And this love is shed abroad in our hearts, not by the sufficiency of our own will, nor by the letter of the law, but by the Holy Ghost who has been given to us.
Source: On the Spirit and the Letter (New Advent)