Hebrews 1:9

iniquity--"unnrighteousness." Some oldest manuscripts read, "lawlessness." therefore--because God loves righteousness and hates iniquity. God . . . thy God--JEROME, AUGUSTINE, and others translate Psa 45:7, "O God, Thy God, hath anointed thee," whereby Christ is addressed as God. This is probably the true translation of the Hebrew there, and also of the Greek of Hebrews here; for it is likely the Son is addressed, "O God," as in Heb 1:8. The anointing here meant is not that at His baptism, when He solemnly entered on His ministry for us; but that with the "oil of gladness," or "exulting joy" (which denotes a triumph, and follows as the consequence of His manifested love of righteousness and hatred of iniquity), wherewith, after His triumphant completion of His work, He has been anointed by the Father above His fellows (not only above us, His fellow men, the adopted members of God's family, whom "He is not ashamed to call His brethren," but above the angels, fellow partakers in part with Him, though infinitely His inferiors, in the glories, holiness, and joys of heaven; "sons of God," and angel "messengers," though subordinate to the divine Angel--"Messenger of the covenant"). Thus He is antitype to Solomon, "chosen of all David's many sons to sit upon the throne of the kingdom of the Lord over Israel," even as His father David was chosen before all the house of his father's sons.

— Jamieson-Fausset-Brown Commentary (public domain)