Psalms 7:16

"His toil shall be turned on his head, and his iniquity shall descend on his pate" [Psalm 7:16]. For he had no mind to escape sin: but was brought under sin as a slave, so to say, as the Lord says, "Whosoever sins is a slave." [John 8:34] His iniquity then will be upon him, when he is subject to his iniquity; for he could not say to the Lord, what the innocent and upright say, "My glory, and the lifter up of my head." He then will be in such wise below, as that his iniquity may be above, and descend on him; for that it weighs him down and burdens him, and suffers him not to fly back to the rest of the saints. This occurs, when in an ill regulated man reason is a slave, and lust has dominion.

These words seem to me to have been fulfilled literally in Ahithophel. At the time of the uprising of Cush, he was a man harboring envy, branded by disgrace, falling out as the watchman, who used his skill to be able to see ahead and predict future events that the affairs of Absalom would fail. Before he himself could be substituted by the men of David, he removed himself, and, withdrawing from the household, he hanged himself with a noose. While he gathered the seeds of evil in his thinking and devised against David whatever he had conceived in his thoughts, he brought forth the same seeds for his own destruction.… These words express the general opinion that as anyone plans evil in his spirit against his neighbor and wishes to harm others and builds a pit for their ruin, he does these things against himself, and his trouble will return on his own head. Each one will cause his own sentence on the day of judgment by his own deeds and will receive the fruits of his own labors.

'His sorrow shall be turned upon his own head, and his iniquity shall come down upon his own crown.' Just as if someone throws a stone on high, and is not careful, and the stone comes down upon his head, he is wounded by his own wound; so too the devil is slain by his own pride, he exalts himself and falls in ruin. 'His sorrow shall be turned upon his own head.' The devil now wishes to lift up his head, but cannot. Why can he not lift up his head? Because his sorrow is turned upon his head, and presses him down. The devil (understand, O mystical reader, according to the rule of the Scriptures) is read in Genesis to be himself the snake, himself the serpent in paradise, himself the serpent who spoke to Eve, who reigns on the earth. He is called a snake, because he clings wholly to the earth. Other animals, though they walk on the earth, yet do not have their whole body lying on the earth; though they have feet on the earth, yet they have another part of the body upward. But the devil, that is, the serpent and the old snake, according to Isaiah, is wholly on the earth: he has both his head and the rest of his body level with the ground. Why do I say all this? Because other animals (understand, O prudent reader), though they cling to the earth, yet desire to withdraw from the earth: but the devil has his head and his tail and his whole middle part clinging to the earth. 'His sorrow shall be turned upon his own head, and his iniquity shall come down upon his own crown.' See what he says: both upon his head, and upon the crown of the head. But since iniquity presses both his head and his crown, where is the devil's repentance? This is the devil's end: 'His sorrow shall be turned upon his own head, and his iniquity shall come down upon his own crown.' Beautifully he said, 'shall come down': for the everlasting punishment will come to him from heaven.