Why was Jesus Christ a minister of the circumcision?

Christ served as a minister of the circumcision—that is, the Jews—for the truth of God. His purpose was to confirm the promises made to the fathers: Abraham, Isaac, and Jacob. This ministry to Israel demonstrated God's faithfulness and pointed back to the Abrahamic Covenant.

Les explains that when Scripture calls Jesus Christ a minister of the circumcision, the circumcision means the Jews. So Christ was a minister of the Jews for the truth of God, and the purpose was to confirm the promises made unto the fathers—Abraham, Isaac, and Jacob. Les then connects this to Genesis chapter 12, where the Abrahamic Covenant is given. Thus the ministry to Israel was rooted in God's covenant promises to the patriarchs. The context also notes that while the Old Testament contains seeds of these truths, the doctrine of Christ's death, burial, and resurrection is not found there.

Romans 15:8

Now I say that Jesus Christ was a minister of the circumcision for the truth of God, to confirm the promises made unto the fathers:

Why did Jesus Christ minister to the Jews?

Jesus Christ ministered to the Jews, the people of circumcision, for the truth of God. His purpose was to confirm the promises made to the fathers—Abraham, Isaac, and Jacob—which are grounded in the Abrahamic Covenant of Genesis 12.