12 “That You may give him patience in days of malice: until the pit be dug up for the ungodly”. Have patience therefore every one, if you are a Christian, in time of malice. Days of malice are those in which the ungodly appear to flourish, and the righteous to suffer; but the suffering of the righteous is the rod of the Father, and the prosperity of the ungodly is their own snare. For because God gives you patience in time of adversity, until the pit be dug up for the ungodly, do not think that the Angels are standing in some place with mattocks, and are digging that great pit which shall be able to contain the whole race of the ungodly; and because ye see that the wicked are many, and say unto yourselves carnally: Truly what pit can contain so great a multitude of the wicked, such a crowd of sinners? Where is a pit of such dimensions, as to contain all, dug? When finished? Therefore God spares them. This is not so: their very prosperity is the pit of the wicked: for into that shall they fall, as it were into a pitfall. Attend, brethren, for it is a great thing to know that prosperity is called a pitfall: “until the pit be dug up for the ungodly.” For God spares him whom He knows to be ungodly and impious, in His own hidden justice: and this very sparing of God, causes him to be puffed up through his impunity....The proud man raises himself up against God: God sinks him: and he sinks by the very act of raising himself up against God. For in another Psalm he thus says, “You have cast them down, while they were being exalted.” He said not, You have cast them down, because they were exalted; or, You have cast them down, after they were exalted; so that the period of their exaltation be one, of their casting down another: but in the very act of their exaltation were they cast down. For in proportion as the heart of man is proud, so does it recede from God; and if it recede from God, it sinks down into the deep. On the other hand, the humble heart brings God unto it from heaven, so that He becomes very near unto it. Surely God is lofty, God is above all the heavens, He surpasses all the Angels: how high must these be raised, to reach that exalted One? Do not burst yourself by enlarging yourself; I give you other advice, lest perchance in enlarging yourself you burst, through pride: surely God is lofty: do thou humble yourself, and He will descend unto you.
13....Do thou rejoice beneath the scourge: because the heritage is kept for you, “for the Lord will not cast off His people”. He chastens for a season, He condemns not for ever: the others He spares for a season, and will condemn them for evermore. Make your choice: do you wish temporary suffering, or eternal punishment? Temporal happiness, or eternal life? What does God threaten? Eternal punishment. What does He promise? Eternal rest. His scourging the good, is temporary: His sparing the wicked, is also temporary. “Neither will He forsake His inheritance.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)