So if two Lutherans marry in the Lutheran church in the presence of a Lutheran minister, the Catholic Church recognizes this as a valid sacrament of marriage. If an Episcopalian man marries a Presbyterian woman before a Justice of the Peace, the Catholic Church recognizes this as a valid sacrament of marriage. This is consistent with our theological understanding of marriage. Indeed how odd it would be if the faith community only recognized the marriages of Roman Catholics as valid sacraments. However, once the Catholic Church recognizes a marriage as a valid sacrament, any question of invalidity must come before a church tribunal.
Marriage is both a private and public reality.
An investigation of validity concerning a Protestant marriage occurs if a subsequent marriage involves a Catholic. The faith community at large is concerned for its individual members. So if two Lutherans marry and subsequently divorce, and the divorced man now wishes to marry a Catholic woman, he is not free to do so. He would only become free if the Church issued a declaration of nullity for his first marriage. Nearly twenty percent of formal marriage cases pending before the Boston Tribunal pertain to marriages of non-Catholic Christians.