Next time you talk to a Protestant and infalliblity comes up. When he begins to complain that no man can be infallible. Ask him, “Isn’t Jesus the head of your church?”
And when he says, “Yes.” Then ask him, “Then why is your church fallible? Is Jesus doing a poor job of heading your church?”
Because, if Jesus is the head of a church, that church is infallible. But if the church is fallible, then Jesus is not the head of that church. Jesus is infallible, therefore He leads infallibly. Or what does it mean to be the head of a church?