CLAIM: The author of Hebrews claims that Psalm 45:6 refers to “the Son” (Heb. 1:8). Is he twisting Scripture here?
RESPONSE: This psalm is addressed to the “King” of Israel (Ps. 45:1), and yet, the psalmist calls the king God (Hebrew elohim)! How can a human king carry this moniker? Only a divine King could rightfully carry this title. Michael Brown tells this anecdote, regarding Psalm 45:
“When I first started studying Hebrew in college, I asked my professor, a very friendly Israeli rabbi, to translate for me the words kis’aka ‘elohim ‘olam wa’ed. He replied immediately, ‘Your throne, O God, is forever and ever,’ explaining, ‘These are praises to the Almighty.’ I then asked him to read the rest of the psalm, clearly addressed to the king, and his face dropped. How could this earthly king be called ‘elohim? To repeat: This is the most natural and obvious meaning of the Hebrew, and no one would have questioned such a rendering had the entire psalm been addressed to God.”
Of course, this title in Psalm 45 is referring to the Davidic king, but Jesus was the son of David (Mt. 1:1) who would fulfill the covenant given to his father David (2 Sam. 7:11-16). In further support of this view, the OT elsewhere predicts the coming of a divine King, who would rescue Israel (Isa. 9:6-7).
How can this refer to Jesus, if the royal king is getting married to a woman?
Clearly, Jesus was never married (see comments on John 20:17). How then can this psalm refer to Jesus, if the royal king gets married in the second half of the psalm (vv.9-17)?
When a NT author cites a messianic psalm, they don’t always mean that everything in the psalm refers to the Messiah. Sometimes, biblical prophecy has a one-to-one correspondence and fulfillment (e.g. Ps. 22; Isa. 53; Dan. 9:24-27; Mic. 5:2). Other times, the NT authors see:
(1) similarities between David and Jesus. The NT authors will show how Jesus was “a greater David.” Instead of showing a one-to-one correspondence, they will show a similarity between the two figures.
(2) unfulfilled promises given to David. The NT authors will notice that promises given to David were never fulfilled in his lifetime, so they must be fulfilled in one of his descendants. In this psalm, the anointed king destroys the enemy nations (v.5) and all the nations praise him (v.17). Clearly, this never happened to David, so the psalm points forward to a descendant of David who would fulfill this promise. Furthermore, in this psalm, the NT authors saw how the son of David would be called “God.” Surely this never happened to David! So one of his descendants would need to fulfill this portion of Scripture. VanGemeren writes, “The psalm has implicit messianic significance. Jesus the Messiah is of the lineage of David. He fulfills the theocratic ideals in his present rule and in his glorious return. The promise of remembrance, perpetuity, and honor given to the Davidic king is particularly applicable to the kingdom of our Lord Jesus Christ. All nations will submit themselves to him (1 Cor 15:24–26; Heb 10:12–13).”
 Brown, Michael L. Answering Jewish Objections to Jesus: Theological Objections. Vol. 2. Grand Rapids, MI: Baker, 2003. 43.
 VanGemeren, W. A. (1991). Psalms. In F. E. Gaebelein (Ed.), The Expositor’s Bible Commentary: Psalms, Proverbs, Ecclesiastes, Song of Songs (Vol. 5, p. 349). Grand Rapids, MI: Zondervan Publishing House.