It finds its merit solely in obedience to the will of God. We do it because the Lord tells us to do it. The inspired apostle speaks, in the context, of the salvation of eight souls in Noah's day by water, and says that in that exact likeness the obedient believer is saved by baptism. The New Testament teaches salvation at the point of baptism, and not before baptism. Simon Peter said that as the water of the flood in Noah's time separated the sinful and the clean world, so also after a true likeness does baptism now save you.
Baptism is the line of demarcation between sin and salvation.
That is law. It is the highest of all laws. It is higher than the law of the mother, or the law of the husband, or the law of the land, or the law of gravity, or even moral precepts. It is a sublime law because God demands it-without rhyme or reason. It is a matter of graciously and spontaneously doing what God tells you to do simply because God tells you to do it.