Because Jesus is the true vine, i.e. the true Israel, all those who claim to belong to God's people but have no faith in Him, or rejects Him as the Messiah, will be cut off or removed, regardless of whether they are Jews by birth or by conversion (i.e., through circumcision). In other words, no one can claim to be part of God's people if they reject Jesus as Lord and Messiah. In contrast, all those who believe in Him (e.g., the disciples), regardless of their ethnicity, will be pruned (or cleansed) so that they will bear more fruit. The word "prune" and "clean" are the same in meaning here. Thus, addressing His disciples, they are already cleaned (or pruned) because they believe in Jesus. All they have to do now is to continue trusting in Him (remain in Him), because that's the only way they can bear fruit (both in terms of their character transformation and their good works).