Children goes to school in uniforms. On their uniform is…

Children goes to school in uniforms. On their uniform is a school badge. On the school badge are symbols, icons and a motto.
Passersby seeing the badge goes “Ah, this child goes to that school.

Water baptism is like that badge. There’s death, burial and resurrection for its symbols. The motto is Unity & Love.
Passersby seeing your baptism goes “Ah, this child is a follower of Jesus.

It isn’t necessary for salvation. But it’s a public declaration of your will to be an ambassador of our Lord. That’s it.