How does the Church define belief? Is doubt a sin?
I can think of two basic ways to define belief. On the one hand, it can be defined objectively, in terms of a person’s tendency to behave. To the extent that, for example, someone was personally committed to act as if Christianity (or Catholicism) were true, he or she would be a believer. This allows for degrees of belief, of course. Someone might be willing to so act up to the point where, say, their life depended upon their renouncing Christianity. Perhaps such a person would not qualify as Christian, whether or not they were ever actually ever in that position. But would you say that someone who WAS willing to sacrifice everything in this world for Christ (or the Church) would not be a Christian (or Catholic) in the fullest sense, if they harbored serious (subjective) doubts about the truth of their religion, but were committed to never acting upon them (aside, perhaps, from admitting their existence)?
On the other hand, we could define belief subjectively, as just an inner sense that something is true, apart from any tendencies toward behavior (though of course behavior would probably follow from the subjective state of belief). Unlike the objective criterion, this seems to make belief less of a decision and more of a happy or unhappy accident. Maybe we can interpersonally compare our subjective belief states about controversial matters by contrasting them with less controversial matters. For instance, some Christians I’ve spoken to affirm that they are as certain that Christianity is true as they are that 1+1=2. More reserved would-be believers might say that they are as certain as they are that the sun will come up tomorrow, or that the moon landing actually took place. I suppose that at a minimum under this criterion it would have to seem more likely to a Christian that a fair coin toss would turn up tails than that Christianity would turn out to be false.
Whether the Church defines belief in one of these two ways, a combination of the two, or in some way I haven’t considered, I’d like to know what is required to 1) be a Christian 2) be a Catholic 3) take the Eucharist. I would also like to know if doubt is a sin, and what doubt consists of in light of the Church’s position on belief, whatever that might be.