Some Pharisees converted to Christ, and they even came to accept the fact that Gentiles could be with them in the church, but Luke revealed this,
“But some of the sect of the Pharisees who believed rose up, saying, ‘It is necessary to circumcise them, and to command them to keep the law of Moses’” (Acts 15:5).
These Pharisees did not yet understand the relationship between the Law of Moses, circumcision, and Christ. Believing these things, circumcision in particular, still applied, they urged Gentiles to do them. This caused a great debate and eventually a delegation was sent to Jerusalem to the apostles and elders there to determine the matter.
While truth still prevails from the Law of Moses, how to carry out that truth has not prevailed, and that is why we can read in the New Testament of apostles quoting the Law of Moses to love God, for example, but that we do not show loving God by keeping circumcision.