Now the chief matter in (or, in regard to) the things which are being said is (or, to sum up what we are saying). The word κεφάλαιον in itself may mean either "summary" or "chief point." It is not "the sum of what we have spoken," as in A.
V. "Caput, id est praecipuum …. dum haec omnia de archisacerdote nostro dicimus, caput totius sermonis, ordine ita postulante, commemorandum venit. Conf. ἐπὶ, Hebrews 8:6; Hebrews 9:10, Hebrews 9:15, Hebrews 9:17; Hebrews 10:28" (Bengel).
We have such a High Priest (i.e. such as has been described; cf. Hebrews 7:26), who sat down on the right hand of the throne of the Majesty (or, of Majesty) in the heavens (cf. Hebrews 1:3, and what was there said).