CLAIM: Amillennial interpreters argue that the church fulfills God’s covenant with Abraham.
RESPONSE: The church is a partial fulfillment of the Abrahamic covenant, but it isn’t a complete fulfillment. The Abrahamic covenant (Gen. 12:1-3) consisted of three major promises:
 many descendants,
 and his offspring would bless the world.
While the church does partially fulfill number two and three, it doesn’t fully fulfill the entire promise. God was clear that this promise was an eternal promise that would be fulfilled in Israel. In Romans 4, it seems that Paul is not saying that the church fulfills this promise given to Israel. Instead, it seems that Paul is simply saying that faith is the key to God’s blessing. The purpose of Romans 4 is justification in the past, rather than prophetic fulfillment in the future (4:2). Paul’s burden in Romans 4 is to show how men were justified by Christ’s first coming, rather than how Jews are included in his second coming. At this point in the letter, Paul is just trying to get his readers to understand justification at the Cross.
Later in the letter (Rom. 9-11), Paul will bring up the subject of God’s promises to Israel. At this point in Romans, Paul is simply trying to show that faith is the key to God’s blessing; he is not making a statement about the OT promises to Abraham being fulfilled in the church. For Paul’s discourse on the OT promises to Israel, flip forward to Romans 11. For further reading on this topic, see “Articles on Eschatology.”