Let him be condemned - רשע יצא yetse rasha . "Let him come out a wicked man;" that is let his wickedness be made manifest.
Let his prayer become sin - Thus paraphrased by Calmet: "Let him be accused, convicted, and condemned, and let the defense which he brings for his justification only serve to deepen his guilt, and hasten his condemnation." I once more apprise the reader, that if these are not the words of David's enemies against himself, (see on Psalm 109:20; (note)), they are prophetic denunciations against a rebellious and apostate person or people, hardened in crime, and refusing to return to God.
When he shall be judged - When for his offences he shall be arraigned. The psalmist supposes that he “might” be put on trial; he seems to suppose that this “would be.” Such wickedness could not always escape detection, and sooner or later he would be arrested and brought to trial. “When” this should occur, the psalmist prays that justice might be done; that he might be condemned, as he “ought” to be. Such a prayer could not in itself be wrong, for assuredly it cannot be proper for magistrates to pray that the wicked man may escape, or that they may themselves fail in the very object for which they are appointed. See the General Introduction, 6 (5) e. f.
And let his prayer become sin - Evidently his prayer in reference to his “trial” for crime; his prayer that he might be acquitted and discharged. Let it be seen in the result that such a prayer was wrong; that it was, in fact, a prayer for the discharge of a bad man - a man who ought to be punished. Let it be seen to be what a prayer would be if offered for a murderer, or violator of the law - a prayer that he might escape or not be punished. All must see that such a prayer would be wrong, or would be a “sin;” and so, in his own case, it would be equally true that a prayer “for his own escape” would be “sin.” The psalmist asks that, by the result of the trial, such a prayer might be “seen” to be in fact a prayer “for the” protection and escape of a “bad man.” A just sentence in the case would demonstrate this; and this is what the psalmist prays for.