To defend the faith, the Christian must use truth, facts, and reason appropriately and prayerfully. The Christian should listen to objections and make cogent and rational comments in direct response to the issues raised.
Logic is simply a tool in the arsenal of Christian apologetics.
Logic is a system of reasoning. It is the principles of proper thinking used to arrive at correct conclusions. Of course, some people are better at thinking logically than others and there is no guarantee that using logic to the best of one's ability will guarantee conversion of anyone. After all, logic is not what saves a person. Jesus does that.