But thou, O God, shalt bring them down into the pit of destruction: bloody and deceitful men shall not live out half their days; but I will trust in thee. But thou, O God, shalt bring them down into the pit of destruction - The Chaldee is emphatic: "And thou, O Lord, by thy Word (במימרך bemeymerach) shalt thrust them into the deep gehenna, the bottomless pit, whence they shall never come out; the pit of destruction, where all is amazement, horror, anguish, dismay, ruin, endless loss, and endless suffering."
Bloody and deceitful men shall not live out half their days - So we find, if there be an appointed time to man upon earth, beyond which he cannot pass; yet he may so live as to provoke the justice of God to cut him off before he arrives at that period; yea, before he has reached half way to that limit. According to the decree of God, he might have lived the other half; but he has not done it.
But I will trust in thee - Therefore I shall not be moved, and shall live out all the days of my appointed time.
The fathers in general apply the principal passages of this Psalm to our Lord's sufferings, the treason of Judas, and the wickedness of the Jews; but these things do not appear to me fairly deducible from the text. It seems to refer plainly enough to the rebellion of Absalom. "The consternation and distress expressed in Psalms 55:4-8, describe the king's state of mind when he fled from Jerusalem, and marched up the mount of Olives, weeping. The iniquity cast upon the psalmist answers to the complaints artfully laid against the king by his son of a negligent administration of justice: and to the reproach of cruelty cast upon him by Shimei, 2 Samuel 15:2, 2 Samuel 15:4; 2 Samuel 16:7, 2 Samuel 16:8. The equal, the guide, and the familiar friend, we find in Ahithophel, the confidential counsellor, first of David, afterwards of his son Absalom. The buttery mouth and oily words describe the insidious character of Absalom, as it is delineated, 2 Samuel 15:5-9. Still the believer, accustomed to the double edge of the prophetic style, in reading this Psalm, notwithstanding its agreement with the occurrences of David's life, will be led to think of David's great descendant, who endured a bitter agony, and was the victim of a baser treachery, in the same spot where David is supposed to have uttered these complaints." - Bishop Horsley.
Commentary on the Bible, by Adam Clarke [1831].