Baptism makes us members of the Christian community, of the Body of Christ. It is not a silly act, but if given to an infant it doesn't "wash away sin."  If given to an adult, yes, it forgives sin in the same way Penance does. 

When I was a kid the Sisters would tell us that Jesus died for our sins and "opened the gates of heaven."  As eight-year-olds we all took this literally, but there are no gates and they were never locked. Jesus came to reform Judaism and to teach us a better way to serve God than by observing 600+ laws. Naturally he made enemies by threatening the powerful and their  status quo and the comfy existence the Temple elites had going.