But baptism in the Protestant faith, in the reformed tradition, is not some kind of a magical bestowing of a blessing. Instead, it s really something that takes place within a church community. If you recall whenever we have a baptism, not only do the parents and god-parents promise that they are going to do their best to raise the child up in the faith, to know and love God so that at some point that child can make a decision for herself whether she want to confirm her faith in the Christian church and become a member of the congregation, but all of you are asked to stand, to represent both this church and the church universal, in promising to aid the parents in raising the child to know and love God. If you are never going to see that child again, it is difficult for you to carry through on those responsibilities. If people request a private baptism, then there is no one to stand up and take those vows at all.
Baptism is very much a communal event.
I believe the same argument can be made for Christianity itself it is a communal activity. We are called on to be the body of Christ, the followers of Jesus, to be the hands and the feet of Jesus, carrying on ministry in this world. That is not to say that you can t be a spiritual person, by yourself. Obviously, you can. You can believe in God by yourself.