The God of peace (ho theos tēs eirēnēs). God is the author and giver of peace, a Pauline phrase (6 times) as in 1Th 5:23.
Who brought again from the dead (ho anagagōn ek nekrōn). Second aorist active articular participle of anagō (cf. Rom 10:7), the only direct mention of the resurrection of Jesus in the Epistle, though implied often (Heb 1:3, etc.).
That great shepherd of the sheep (ton poimena tōn probatōn ton megan). This phrase occurs in Isa 63:11 except ton megan which the author adds as in Heb 4:14; Heb 10:21. So here, “the shepherd of the sheep the great one.”
With the blood of the eternal covenant (en haimati diathēkēs aiōniou). This language is from Zec 9:11. The language reminds us of Christ’s own words in Mar 14:24 (Mat 26:28; Luk 22:20; 1Co 11:25) about “my blood of the covenant.”