15 And for this reason He is the Mediator of the new covenant, by means of death, for the redemption of the transgressions under the first covenant, that those who are called may receive the promise of the eternal inheritance.
16 For where there is a testament, there must also of necessity be the death of the testator.
17 For a testament is in force after men are dead, since it has no power at all while the testator lives.
18 Therefore not even the first covenant was dedicated without blood.
19 For when Moses had spoken every precept to all the people according to the law, he took the blood of calves and goats, with water, scarlet wool, and hyssop, and sprinkled both the book itself and all the people,
20 saying, “This is the blood of the covenant which God has commanded you.”
21 Then likewise he sprinkled with blood both the tabernacle and all the vessels of the ministry.
22 And according to the law almost all things are purified with blood, and without shedding of blood there is no remission.
The word “mediator” is the translation of mesites which refers to one who intervenes between two, either to make or restore peace and friendship, to form a compact, or to ratify a covenant. Here the Messiah acts as a go-between or mediator between a holy God and sinful man. — Hebrews in the Greek New Testament, by Kenneth S. Wuest, pages 162-163.
for this reason (v.15) — because Christ’s blood accomplished what the Old Covenant could not do — He brought redemption, even for sins committed under the Old Covenant. (the Old Testament sacrifices only made a covering for sin — atonement
The Old Testament sacrifices might be compared to the writing of a check. The paper upon which it is written is practically worthless. Yet, it is used and accepted in place of money, since it is backed by what has been deposited in the bank. Christ’s death was deposited from the foundation of the world as that which backed the Old Testament sacrifices. With Christ’s death upon the cross, the deposit was released and all the past checks were honored and paid. — KJV Commentary, page 1696.
testament (v.16) — same word as “covenant (8:6-7) = lit. “to place between two”
In every place in Hebrews except 9:16-17, diatheke refers either to the Levitical sacrificial system or to the sacrifice of the Messiah. The word refers to the disposition of eternal life to the recipient on the basis of his acceptance of the atoning merits of the latter sacrifice. In the sense that the word diatheke refers to the act of God as one party making a disposition to another on specified terms, the word means “a covenant.” But when the substitutionary death of the One making the disposition is brought into the picture, the idea of a covenant is merged with that of a will or testament. Since the new covenant was made effective through theh death of the Testator, the Messiah, and since the first covenant is typical of the new, both covenants take on themselves the idea of a last will or testament. The present writer has, therefore, translated diatheke uniformly in Hebrews by the word “testament” in the sense which the writer to the Hebrews gives it in 9:16-17.
The word “inheritance” in 9:15″ leads the inspired penman to define the context of diatheke as it is used in this epistle. An inheritance involves the idea of someone making a disposition of his property, the heir receiving same at the death of the testator. Just as in human relationships, where a will or testament is of force only after the one who makes the will is dead, so in the case of God bequeathing salvation to the lost sinner, the bequest is only operative by reason of His death. Thus, in verse 15, the writer speaks of the Messiah as the Mediator of the New Testament who made that Testament effective through His death, and in that way, lost sinners who accpet salvation on the terms of the will or testament come into their inheritance. — Wuest, page 165.
These verses in Hebrews declare that the book of Matthew has no part in Israel’s New Testament prior to chapter 27:50. In Mark the Old Testament runs through chapter 15:41, in Luke it is chapter 23:49 and finally, in John, Old Testament doctrine operated through 19:37. It is at those verse locations where we find the death of the testator, the Lord Jesus Christ; and these verses in Hebrews teach that the New Testament cannot exist before those points. — M.A.D. about Hebrews, by Terence D. McLean, page 124.
Even the Old Testament, incomplete though it was, required blood (v.18).
blood of calves (v.19) — Exodus 24:5-6
water (v.19) — Leviticus 14:4-7; Numbers 19:18
likewise (v.21) — at a later time (the tabernacle hadn’t yet been built)
almost (v.22) — not all sins could be atoned for under the law (Numbers 15:30-31 for example) or by fire and water (Numbers 31:22-23)