Revelation 5:5

one of--Greek, "one from among." The "elder" meant is, according to some (in LYRA), Matthew. With this accords the description here given of Christ, "the Lion, which is (so the Greek) of the tribe of Juda, the root of David"; the royal, David-descended, lion-aspect of Christ being that prominent in Matthew, whence the lion among the fourfold cherubim is commonly assigned to him. GERHARD in BENGEL thought Jacob to be meant, being, doubtless, one of those who rose with Christ and ascended to heaven (Mat 27:52-53). The elders in heaven round God's throne know better than John, still in the flesh, the far-reaching power of Christ. Root of David-- (Isa 11:1, Isa 11:10). Not merely "a sucker come up from David's ancient root" (as ALFORD limits it), but also including the idea of His being Himself the root and origin of David: compare these two truths brought together, Mat 22:42-45. Hence He is called not merely Son of David, but also David. He is at once "the branch" of David, and "the root" of David, David's Son and David's Lord, the Lamb slain and therefore the Lion of Juda: about to reign over Israel, and thence over the whole earth. prevailed--Greek, "conquered": absolutely, as elsewhere (Rev 3:21): gained the victory: His past victory over all the powers of darkness entitles Him now to open the book. to open--that is, so as to open.

— Jamieson-Fausset-Brown Commentary (public domain)