Hebrews 8:6 has the Greek term mesitēs (“mediator”), which is derived from mesos (“middle”) and denotes the one who walks or stands in the middle. It was a technical term that referred to a person who fulfilled one or more of the following functions: (1) an arbiter between two or more parties; (2) a negotiator or business broker; (3) a witness in the legal sense of the word; or (4) one who stands as a surety and, thus, guarantees the execution of an agreement.
The English term “mediator” is too narrow a translation for mesitēs in Hebrews because it focuses only on the first two or three uses of the Greek term. Hebrews, however, emphasizes the fourth function. Jesus is not conceived as a mediator in the sense that He settles a dispute between the Father and humans, or as a peacemaker who reconciles parties in disaffection or as a witness that certifies the existence of a contract or its satisfaction. Instead, as Hebrews explains, Jesus is the guarantor (or surety) of the new covenant (Heb. 7:22). In Hebrews, the term “mediator” is equivalent to “guarantor.” He guarantees that the covenant promises will be fulfilled.
Christ’s death makes the institution of the new covenant possible because it satisfies the claims of the first covenant with Israel (and even with the first humans in Eden), which had been broken (Heb. 9:15–22). In this sense, Jesus is the guarantor who took upon Himself all the legal obligations of the covenant that had been broken. In another sense, Jesus’ exaltation in heaven guarantees that God’s promises to human beings will be fulfilled (Heb. 6:19, 20). Jesus guarantees the covenant because He has shown that God’s promises are true. By resurrecting Jesus and seating Him at His right hand, the Father has shown that He will resurrect us and bring us to Him.
Jesus is a greater Mediator than Moses because He ministers in the heavenly sanctuary and has offered Himself as a perfect sacrifice for us (Heb. 8:1–5; 10:5–10). Moses’ face reflected the glory of God (Exod. 34:29–35), but Jesus is the glory of God (Heb. 1:3; John 1:14). Moses spoke with God face to face (Exod. 33:11), but Jesus is God’s Word personified (Heb. 4:12, 13; John 1:1–3, 14).
We may be tempted to think that in Hebrews 8:6 the new covenant has “better promises” in the sense that it has greater rewards than the old covenant had (a heavenly homeland, eternal life, and so on). The truth is that God offered the same rewards to Old Testament believers as He has offered us (read Heb. 11:10, 13–16). The “better promises” is talking about different kinds of promises.
The covenant between God and Israel was a formal exchange of promises between God and Israel. God took the initiative and delivered Israel from Egypt and promised to lead them into the Promised Land.
The covenant between God and Israel was ratified with blood. This blood was sprinkled both over and beneath the altar. The people of Israel promised to obey all that the Lord had spoken.
God satisfies the absolute demands of the new covenant for us because He gave His own Son to come and live a perfect life so that the promises of the covenant might be fulfilled in Him, and then offered to us, by faith in Jesus. Jesus’ obedience guarantees the covenant promises (Heb. 7:22). It requires that God gives Him the blessings of the covenant, which are then given to us. Indeed, those who are “in Christ” will enjoy those promises with Him. In addition, God gives us His Holy Spirit to empower us to fulfill His law.