Question 39: Why do we re-baptize Protestants when they enter the Church?

Answer: We do not re-baptize them, as Baptism can be received only once. We baptize converts conditionally, only when a prudent doubt exists about the validity of the former baptism. The form is: "If you are not baptized, I baptize you..." etc. If the first Baptism was valid, the conditional Baptism is not a Sacrament.