Commentators differ as to whether the act of begetting the Son in these two passages is
(a) the eternal generation, or
(b) the incarnation in time, or
(c) the resurrection and ascension.
The immediate context of Heb 1:5 (see Heb 1:3) seems to favor the last view (Westcott). The first view would not be foreign to the author’s thought: with Heb 5:5 compare Heb 6:20, "a high priest forever" (Alford). The author of Heb thinks of the eternal and essential sonship of Christ as realized in history in His ascension to the "right hand of the Majesty" (Heb 1:3). And what is emphatic is the fact and status of sonship, rather than the time of begetting.