One may ask why the Jews would wear phylacteries on their forehead and their arms. What good does it do to wear scripture on your forehead or on your arm? Well God in the scripture said to. But just as there is a physical to spiritual reason in why the Jews wear these odd boxes on their bodies... there is the same with baptism. There are many things in the bible that have a physical slide to spiritual double meaning. Much like communion. The bible says to do this in remembrance of Me. Will you be sinning because you missed communion because you were home sick that day? No. Because in the Spirit, both baptism and communion go with us where ever we go, now that Jesus died for our sins and we accept what He did. His Spirit lives in us. Doing such things in the flesh is done in obedience and strengthens us as it reminds us to look to the Spirit when we are weak.
If we are not careful, we will do just like the Jews did and add so many laws to doing this baptism just perfect that we miss the whole point of doing it in the first place. There is much freedom when we walk in the Spirit.