This excerpt is from a sermon by Charles Haddon Spurgeon entitled "The Blood of the Covenant," delivered August 2, 1874.
"In olden times when men made covenants the one with the other, they generally used some ceremony to bind the bargain, as it were. Now, under the old dispensation covenants with God were always confirmed with blood. As soon as ever blood was shed, and the victim died, the agreement made was established. Now, when our heavenly Father made a covenant with Jesus Christ on our behalf, that covenant was true and firm, “according to the sure mercies of David,” but to make it stand fast there must be blood. Now, the blood ordained to seal the covenant was not the blood of bulls or of goats, but the blood of the Son of God Himself; and this has made the covenant so binding that sooner may heaven and earth pass away than one tittle of it fail.
God must keep His own promises. He is a free God, but He binds Himself; by two immutable things wherein it is impossible for Him to lie, He has bound Himself to bestow covenant blessings upon the flock which the great Shepherd represented. Brethren, you and I, as honest men, are bound by our word. If we took an oath, which I trust we would not, we should certainly feel doubly bound by it; and if we had lived in the old times, and blood had been sprinkled on an agreement which we had made, we should regard the solemn sign and never dream of running back from it.
Think, for a moment, how impossible it is that the Lord should ever break that covenant of grace, which He spontaneously made with his own Son, and with us in Him, now that it has been sprinkled with blood from the veins of his own well-beloved Son. No; the covenant is everlasting. It stands fast for ever, because it is confirmed by blood which is none other than the blood of the Son of God."