Psalms 110:4

4. This contains the grand central revelation of this psalm, the doctrine of the union of priest and king in him whom David calls, (Psalms 110:1,) “my Lord.”

The Lord hath sworn Jehovah hath sworn. A solemn introduction to the glorious oracle about to be uttered.

Will not repent Will not alter his purpose or change his mind. In some things, made conditional from the beginning, he might reverse or modify his administration, as in Genesis 6:6; 1 Samuel 15:11; 1 Samuel 15:29; Jeremiah 18:8, but this fundamental plan of redemption cannot be reversed.

Thou art a priest for ever after the order of Melchizedek The oracle and the decree stand against the whole economy of Moses, which carefully and positively separated the two offices, and are in advance of all revelation concerning Messiah hitherto given. It is the central doctrine and mystery of the redemptive scheme, now first announced. Melchizedek, a primitive patriarch, was both priest and king, (Genesis 14:18;) the type of Christ existed before the Aaronic priesthood, as the great Prototype did at its close. The whole is explained and enforced by the author of the Epistle to the Hebrews, chapter 7, where see notes.

For ever Hebrew, To eternity. The subject demands the fullest import of the word. After the order, means according to the rank, or grade, of which Melchizedek is the type, in contrast with the order of Aaron.