Great question, and it's one that has been around for a while. There are two different views on baptism. The first view comes from the Reformed tradition (the one embraced by your CRC church). In this view, baptism is a sign of God's covenant, or promise. There is a parallel to circumcision in the Old Testament, whereby a baby or young child was marked, or set apart, for God. Similarly, baptism in the Reformed tradition sets the infant or young child apart for God. It is not a sign of salvation, but a symbol of the promise of God and of the commitment of God's people to nurture that child so that he or she will come to know God personally.

The other main view of baptism is the Anabaptist view (Anabaptist means "twice baptized"). The Anabaptists believed that infant baptism wasn't good enough, because baptism was meaningful only if the person being baptized had made a commitment to Jesus already. So the Anabaptists thought that anyone who had been baptized as an infant needed to be baptized again as a believing adult.

In this view, baptism is a sign of salvation. It shows identity with Christ.

I think both views are valid, and one view doesn't negate the other. In your case, if you have been baptized as a baby, you don't need to be baptized again. Not all churches agree with this (as you have discovered), so you have to make a decision as to whether or not you want to follow the protocol of the church you are currently attending.

In either case, baptism is not necessary for salvation, and it is not a guarantee of salvation. Where infant baptism is concerned, it is a symbol of God's love and commitment to us. Where adult baptism is concerned, baptism is the outward sign of inward regeneration, and a symbol of our commitment to Him.