The Catechism in Questions & Answers

406. Do all baptised individuals belong to the church of Jesus Christ?

All people who believe in Jesus Christ and profess the Son of God as their Lord are part of the church of Christ. They are baptised in the name of the triune God, the Father, the Son, and the Holy Spirit.
But by far not all the baptised believe and profess. Accordingly, not all who are baptised belong to the church of Christ.