Ellicott's Commentary On The Whole Bible
Psalms 110 - Introduction
CX.
At the first sight the authorship and purpose of this psalm are, for a Christian expositor, not only placed beyond the necessity of conjecture, but even removed from the region of criticism, by the use made of its first verse by our Lord, and the emphatic manner in which He quotes it as the Divinely inspired utterance of David (Matthew 22:41; Mark 12:35; Luke 20:41). But it is now, even among the most orthodox, an admitted fact that, in matters of literature and criticism, our Lord did not withdraw Himself from the conditions of His time, and that the application He made of current opinions and beliefs does not necessarily stamp them with the seal of Divine authorisation.
The prominent thought in the psalm is the formal union in one person of the royal dignity and the priesthood. Now all the kings of Israel and Judah at times assumed priestly functions, but only twice in the history can the offices be said to have been formally combined — in the person of Joshua son of Josedech (Zechariah 11:12), and in that of the Asmonean Jonathan and his successors (1Ma. 11:57). The latter reference is preferable. The impression left by the psalm is exactly in accordance with the history of the Asmoneans. One whom Jehovah has declared by solemn oath a priest; one, i.e., in whom the priesthood was indubitably and firmly fixed, is exalted at Jehovah’s right hand as a king, and, as a warrior, rides on with Jehovah to triumph. And the choice of Melchizedek, as type (see Note, Psalms 110:4), does not arise from any idea of contrasting his order with that of Aaron, but from the necessity of going back to him for an instance of actual and formal priesthood combined in the same person, with kingly rank. In 1Ma. 14:41 the very expression of the psalm, “high priest for ever,” is used of Simon.
The abrupt ending of this short psalm has led many critics to regard it as a fragment. The parallelism is very lax.