The linen would change colors. The iron would become cool. So when baptism began being practiced in religious circles, it must have originally carried this same sort of mystical meaning with it too. When a person was placed into and under the water, that water was thought of as either physically being able to create some sort of spiritual change in the person, or became a symbolic representation of a change that had already taken place. Now what the Bible seems to teach concerning water baptism of those who choose to follow Jesus is that the water of baptism is not itself mystical in that it creates some sort of actual change, besides making the person wet, but that it is highly symbolic of a real change that has already taken place.
Baptism is an external expression of an internal surrender to the love and leadership of Jesus.
And as such, it is really a public statement of one's intent to follow Jesus for the rest of their lives. In a real way, baptism is to my relationship with Jesus what my wedding ring is to my marriage. My wedding ring doesn't make me married. I'm married whether I'm wearing my ring or not. If I lose it, I'm still married.