For all the promises of God in Him are yea, and in Him Amen, unto the glory of God by us. – 2 Corinthians 1:20

Beloved, in a covenant there are pledges given, and on those pledges we delight to meditate. You know what they were. The Father pledged His honour and His word. He did more; He pledged His oath; and “because He could swear by no greater, He sware by Himself.” He pledged His own word and sacred honour of Godhead that He would be true, to His Son, that He should see His seed; and that by the knowledge of Him Christ should “justify many.” But there was needed a seal to the covenant, and what was that Jesus Christ in the fulness of time set the seal to the covenant, to make it valid and secure, by pouring out His life’s blood to make the covenant effectual once for all. Beloved, if there be an agreement made between two men, the one to sell such-and-such an estate, and the other to pay for it, the covenant does not hold good until the payment is made. Now, Jesus Christ’s blood was the payment of His part of the covenant; and when He shed it, the covenant stood firm as the everlasting hills, and the throne of God Himself is not more sure than is the covenant of grace; and, mark you, that covenant is not sure merely in its great outlines, but sure also in all its details. Every soul whose name was in that covenant must be saved. Unless God can undeify Himself, every soul that Christ died for He will have. Every soul for which He stood Substitute and Surety He demads to have, and each of the souls He must have, for the covenant stands fast. Moreover, every blessing in which that covenant was guaranteed to the chosen seed was by the precious blood made eternally secure to that seed. Oh, how I delight to speak about the sureness of that covenant! How the dying David rolled that under his tongue as a sweet morsel! “Although my house,” said he, “be not so with God,”-there was the bitter in his mouth; “yet,” said he, and there came in the honey, “yet He hath made with me an everlasting covenant, ordered in all things, and sure.” And this sureness, mark you, lies in the blood; it is the blood of Christ that makes all things secure, for all the promises of God are yea and amen in Christ Jesus, to the glory of God by us.~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/3293.cfm