What does is a spiritual act mean in catholicism or other religions?

It's a spiritual thing in the fact that it bonds two people together eternally. God created so that two married people can have fun within their relationship. But he also created it to make the bond within marriage stronger. is something that is fun, relieves stress, and there it's not like it has to be taken completely serious to the point where it's not supposed to be fun but it is very spiritual in that it creates a bond between two people.