You do not support the root, but the root supports you: When Paul wrote to the church in Rome, most of its members were not Jewish. This was common in many early Christian communities.
Because Gentiles had become the majority, some began to boast about their place in God’s people. Some also looked down on Jews and on Israel’s religious heritage. Paul corrects this attitude. He reminds Gentile believers that they share in God’s blessings only because they have been joined to God’s people. That people is rooted in God’s promises to Israel.