Behold, the days come, saith the LORD, that I will make a new covenant – Jeremiah 31:31

The covenant of works was made with the race in the first Adam; but the first Adam was faulty and failed full soon; he could not bear the stress of his responsibility, and so that covenant was broken. But the surety of the new covenant is our Lord Jesus Christ; and He is not faulty, but perfect. The Lord Jesus is the federal Head of His chosen, and He stands for them: they are regarded as members of His body, and He is their head, their mouthpiece, their representative. The Lord Jesus, as the second Adam, entered into covenant with God on the behalf of His people; and because He cannot fail-for in Him there is no infirmity or sin-therefore the covenant of which He is the surety must stand. He abideth for ever in His Melchizedek priesthood, and in the power of an endless life. He is, both in His nature and in His work, eternally qualified to stand before the living God. He stands in absolute perfectness under every strain, and, therefore, the covenant stands in Him. When it is written, “I have given Him for a covenant to the people,” we see that the covenant cannot fail, because He cannot fail who is the sum and substance of it. Because the Lord Jesus represents all His believing people in the covenant, therefore the covenant is everlasting.

Faith in the everlasting covenant stirs my heart’s blood, fills me with grateful joy, inspires me with confidence, fires me with enthusiasm. I can never give up my belief in what the Lord hath said, “And I will make an everlasting covenant with them, that I will not turn away from them, to do them good; but I will put My fear in their hearts, that they shall not depart from Me.” ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/2108.cfm