In Hebrews 9:15 and 12:24 Christ is styled “the mediator of the new covenant

Once more, in Hebrews 9:15 and 12:24 Christ is styled “the mediator of the new covenant,” because it is by His efficacious satisfaction and prevailing intercession that all its blessings are now imparted to its beneficiaries. Christ now stands between God and His people, advocating their cause (1 John 2:1) and speaking a word in season to him that is weary Isa. 50:4). But how could Christ sustain such offices as these unless the covenant had been made with Him (Gal. 3:17) and the execution of it had been undertaken by Him (Heb. 10:5-7)? “Now the God of peace, which brought again from the dead our Lord Jesus, that great shepherd of the sheep, through the blood of the everlasting covenant” (Heb. 13:20): that one phrase is quite sufficient to establish the fact that an organic connection existed between the covenant of grace and the sacrifice of Christ. In response to Christ’s execution of its terms, the Father now says to Him, “By the blood of thy covenant I have sent forth thy prisoners those given to Him before the foundation of the world, but in Adam fallen under condemnation) out of the pit wherein is no water” (Zech. 9:11).

Arthur W. Pink- The Divine Covenants-Part One-The Everlasting Covenant