It remains, then, that the church founded in the covenant, and unto which all the promises did and do belong, abode at the coming of Christ, and doth abide ever since, in and among those who are the children of Abraham by faith. The old church was not taken away, and a new one set up, but the same church was continued, only in those who by faith inherited the promises. Great alterations, indeed, were then made in the outward state and condition of the church; as,—
(1.) The carnal privilege of the Jews, in their separation to bring forth the Messiah, then failed; and therewith their claim on that account to be the children of Abraham.
(2.) The ordinances of worship suited unto that privilege expired and came to an end.
(3.) New ordinances of worship were appointed, suited unto the new light and grace then granted unto the church.
(4.) The Gentiles came in to the faith of Abraham together with the Jews, to be fellow-heirs with them in his blessing. But none of these, nor all of them together, made any such alteration in the church but that it was still one and the same. The olive-tree was the same, only some branches were broken off, and others planted in; the Jews fell, and the Gentiles came in their room.
John Owen, An Exposition of the Epistle to the Hebrews, 1.124. Emphasis added.
The new covenant is simply the realization of the covenant God made with Abraham, when God walked alone between the pieces, promising that God himself would provide the perfect obedience that we cannot provide and die as the penalty of our transgressions. Abraham believed God’s promise and it was counted to him as righteousness. The same is true of all his children who trust in the God who redeems His people by doing all the covenant requires, as their representative. We do not do our part of the covenant by our flawed obedience, but we do demonstrate our love and thankfulness to God by our obedience. God says, because I HAVE brought you out of the land of Egypt/redeemed you, therefore obey my commandments.