Baptism is not a private affair. In Ephesians 4:4-5, Paul provides a list of things that unite God’s family as one and he includes baptism: “There is one body and one Spirit—just as you were called to the one hope that belongs to your call— one Lord, one faith, one baptism, one God and Father of all, who is over all and through all and in all.”
Baptism is a sign of “publicly and formally” being committing to and being enfolded into the family of God. As we are united with Christ, we are united with the Church.