Christianity is a life, not a doctrine . . . I'm not saying never doubt or question. The Lord gave you a mind so that you would make honest use of it. I'm saying you must be sure that the doubts and questions are your own.
People who feel any sort of regret where you are concerned will suppose you are angry, and they will see anger in what you do, even if you're just quietly going about a life of your own choosing. They will make you doubt yourself, which, depending on cases, can be a severe distraction and a waste of time. This is a thing I wish I had understood much earlier than I did.
Religion, if it is genuine, is so profoundly interwoven with individual thought and experience that it is no more exhaustible than consciousness itself. And fiction whose purpose is didactic is bad no matter whether the matter to be "taught" is Christianity or the world view of Ayn Rand. It seems often to be assumed by writers that religion is a pose, meant to deceive oneself or others, or that it is a bad patch on doubt or complexity. This is only convention, however. The writers I know have a much deeper engagement with the real issues of religion.
Sometimes my doubt seems intuitive, but most likely it derives from an implausibility or a logical problem I may at first find difficult to identify and articulate. It is interesting to me to work through questions that arise in this way.