Are you suggesting that we don't have to be found in Christ to be in covenant with God?
Some interesting things to note regarding the covenant with Abraham and how it was realized in Christ (speaking of the birth of Christ)...
He has helped his servant Israel, in remembrance of his mercy, as he spoke to our fathers, to Abraham and to his offspring forever." (Luk 1:54-55)
"Blessed be the Lord God of Israel, for he has visited and redeemed his people and has raised up a horn of salvation for us in the house of his servant David, as he spoke by the mouth of his holy prophets from of old, that we should be saved from our enemies and from the hand of all who hate us; to show the mercy promised to our fathers and to remember his holy covenant, the oath that he swore to our father Abraham, to grant us (Luk 1:68-73)
Peter speaks of the salvation from Jesus as being a fulfillment of the covenant to Abraham that all nations would be blessed through him...
You are the sons of the prophets and of the covenant that God made with your fathers, saying to Abraham, 'And in your offspring shall all the families of the earth be blessed.' God, having raised up his servant, sent him to you first, to bless you by turning every one of you from your wickedness." (Act 3:25-26)
Paul says that when God said all nations would be blessed through Abraham that He would justify the Gentiles by faith and was announcing the Gospel ahead of time to Abraham (Gal 3:8). So he says that all beleivers are blessed along with Abraham (Gal 3:9)...
And the Scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel beforehand to Abraham, saying, "In you shall all the nations be blessed." So then, those who are of faith are blessed along with Abraham, the man of faith. (Gal 3:8-9)
We also read of Christ confirming the promises given to the patriarchs...
For I tell you that Christ became a servant to the circumcised to show God's truthfulness, in order to confirm the promises given to the patriarchs, and in order that the Gentiles might glorify God for his mercy. As it is written, "Therefore I will praise you among the Gentiles, and sing to your name." (Rom 15:8-9)
We further read that it is in Jesus that the blessing of Abraham comes to the Gentiles so that we (Jews and Gentiles) might receive the promise...
Christ redeemed us from the curse of the law by becoming a curse for us--for it is written, "Cursed is everyone who is hanged on a tree"-- so that in Christ Jesus the blessing of Abraham might come to the Gentiles, so that we might receive the promised Spirit through faith. (Gal 3:13-14)
Thus the covenant with Abraham and the promises given in it are fulfilled in Christ and those that are found in Him.