A Scenario and a Question

In the rite of confirmation, a 13-year-old is received into communicant membership on account of his professed agreement with Luther’s Small Catechism.

Decades later, he starts reading another part of the Book of Concord and comes across a seemingly minor assertion that is not substantiated by a Bible reference and not found anywhere in the Small Catechism. He determines that he cannot in good conscience agree with that particular assertion in light of some Bible verses that he can readily cite. And there he stands; he can do no other.

This man is an active lay member of an LCMS congregation. Should he resign his membership?