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I sometimes hear Christians say that the old covenants have been done away in Jesus Christ - that God made a covenant with Noah, Abraham, Moses, and David, but that those covenants were superseded by the covenant we have with God through the death and resurrection of Christ. I understand that thinking and can even see some truth in the details of what proponents of this position maintain. But the reality is that the Bible doesn't think about God's covenants this way; instead, the Bible finds their ongoing reality in Jesus Christ himself.
A good example of this is Psalm 89:35, which says in the original Hebrew: "Once I swore in my holiness; I am not lying to David." Psalm 89 is a celebration of the covenant God made with David. It seems to have been written by David, and it repeatedly details in various ways how God had chosen David as king over his people and made a covenant of love with him. The specific context of v. 35 discusses the Davidic covenant in the face of potential disloyalty to God exhibited by David's descendants: if the kings of David's line end up being unfaithful to God and breaking this covenant, God will still keep his covenant promises and remain true to David and his heirs (vv. 30-37). The reason for God's covenant faithfulness to David and his descendants is given in v. 35: God's holiness. God did not merely swear an oath to David, he swore one within his holiness; God did not merely promise to tell David the truth, he promised not to lie to David - because God is holy. Apparently, God promised to remain faithful to the covenant he made with David, even if David and the kings after him decided to break faith with God, because God's holiness means that God will not break faith with those he has chosen and loves.
This is good news, friends, because God's faithfulness to the Davidic covenant has been supremely demonstrated in Jesus Christ. As a human descendant of King David, Jesus is the true heir and successor to David's throne - and thus the true recipient, on our behalf, of God's covenant promises to David. God's holiness in the past meant that he would not forsake David if David abandoned him. God's holiness in the present means that he has established Jesus Christ, the son of David, as the one who is worthy to sit on David's throne, as well as the rightful ruler of God's people.
Let us always remember, brothers and sisters, that God's holiness results in our salvation and our acceptance by God.