1:5a Ps 2:7, where God addresses the king on David's throne in words whose full meaning becomes real and apparent in the Son of David, the Son of God.
1:5b 2 Sm 7:14. God's promise to David (through the prophet Nathan) concerning David's successors, a promise fully fulfilled in Jesus Christ.
1:6 Words which in their original settings (Dt 32:43) called upon the angels to worship the Lord God of Israel as the Avenger and Savior of His people are here applied to the incarnate Son of God, "that all may honor the Son, even as they honor the Father" (Jn 5:23). The OT is quoted according to the Septuagint (an ancient Greek translation of the OT), which differs from the one reproduced in English versions. Recent discoveries indicate that this reading may well be the original one.
1:7 Ps 104:4 God's angels ("messengers") appear in various forms, fulfill their service, and vanish. God's Son endures unchanged. (1:8-10)
1:8-9 In Ps 45:6-7 the anointed king of God's people is, as God's vice-regent and executor of His righteousness on earth, called God (or his reign is marked as divine, cf. RSV note a): being under the favor of God, his reign is destined to endure. This ancient promise found its final Yes in Jesus Christ. (2 Co 1:20)
1:10 Ps 102:25-27. Ps 102 is entitled "A prayer of one afflicted, when he is faint and pours out his complaints before the LORD." The psalmist, his existence shattered, can find grounds for hope only in the God who endures when all else passes away. He will arise and have pity on His people, so that all "nations will fear the name of the LORD, and all the kings of the earth" will bow before His glory (Ps 102:12-15). In Jesus Christ God did arise and lead all peoples to worship Him; and the words of Ps 102 are fitly applied to the Son.
1:13 Ps 110:1. God addresses His anointed king. It was with the words of this psalm that Jesus Himself had stated that His Messianic claim most powerfully. (Cf. Mt 22:41-46 note)"
Martin Franzmann and Walter H. Roehrs, Concordia Self-study Commentary [commentary on Hebrews], p. 238