14 Or “swears, vows.”
15 Or “will not change his mind.” The negated Niphal imperfect of נָחַם (nakham) is a way of marking an announcement as an irrevocable decree. See 1 Sam 15:29; Ezek 24:14, as well as R. B. Chisholm, “Does God ‘Change His Mind’?” 152 (1995): .
16 You are an eternal priest. The Davidic king exercised a non-Levitical priestly role. The king superintended Judah’s cultic ritual, had authority over the Levites, and sometimes led in formal worship. David himself instructed the Levites to bring the ark of the covenant to Jerusalem (1 Chr 15:11–15), joined the procession, offered sacrifices, wore a priestly ephod, and blessed the people (2 Sam 6:12–19). At the dedication of the temple Solomon led the ceremony, offering sacrifices and praying on behalf of the people (1 Kgs 8).
17 The phrase עַל־דִּבְרָתִי (’al-divratiy) is a variant of עַל־דִּבְרָת (’al-divrat; the final yod [י] being an archaic genitival ending), which in turn is a variant of עַל דָּבַר (’al davar). Both phrases can mean “concerning” or “because of,” but neither of these nuances fits the use of עַל־דִּבְרָתִי in Ps 110:4. Here the phrase probably carries the sense “according to the manner of.” See L. C. Allen, Psalms 101–150 (), .
18 The Davidic king’s priestly role is analogous to that of Melchizedek, who was both “king of Salem” (i.e., Jerusalem) and a “priest of God Most High” in the time of Abraham (Gen 14:18–20). Like Melchizedek, the Davidic king was a royal priest, distinct from the Aaronic line (see Heb 7). The analogy focuses on the king’s priestly role; the language need not imply that Melchizedek himself was “an eternal priest.”