1: Jesus commanded the disciples to batize all the nations. Babies are members of the nations. Babies should be baptized.

2: Jesus commanded all disciples to be bapized into discipleship. Parents are to disciple their children from birth. Their babies should, therefore, be baptized.

3: God arranged for the Israelites to undergo many cleansings, which the author of Hebrews calls baptisms. There is a contrast between the many washings and our once-and-for-all baptism. All the evidence indicates that Israelite babies could become unclean and need cleansing. So they should instead now be given the once-and-for-all cleansing that is baptism.

Buy Why Baptize Babies: An Explanation of the Theology and Practice of the Reformed Churches (scroll down). Buy it for yourself or buy it for friends.