Here’s my $0.02, not being a theologian or anything, but knowng a bit about psychology. Sorry this is so long, but I started typing and it just kept coming.
There are more than one kind of belief. One kind is the belief of the intellect, which says, “I understand that this is correct based on thus and such.” Another is the belief of the emotions, over which we have little control.
For the first kind of belief, you could say, “I believe in the Real Presence because Jesus told us in John 6 and at the Last Supper that it was true, and also because the Church, which is Christ’s body on Earth, tells me it is true.” However, there are counter arguments that are troubling to some, perhaps many, and besides it is not possible to understand the Real Presence in the same way it is possible to understand, say, the multiplication tables.
It’s a little more, to my mind, like understanding the periodic table, where when you first hear of it, usually as a child, you have a childish and inaccurate, but nonetheless useful and not entirely misleading, picture of atoms as something like a solar system, with well-defined and visible dots moving in perfect circles around a sort of lump of a nucleus. This mental picture gives some idea, and it’s good enough to understand why some ions are formed, and other things about the composition of molecules. But later (I understand, not at all being a chemist), you come to understand it in more detail and (in a sense) more mystery, with its increased complexity. It requires learning, and willingness to admit that the real picture, although it can be “understood” mathematically, will never be as easy to accurately and visually understand as the simpler picture you first learned.
The Real Presence is similar. The problem is, people sometimes aren’t willing to go past the childish picture, even though they can see it is childish. So they say things like “The idea of the Real Presence can’t be true, because the Host is still subject to decay, just like ordinary bread.” Then they hear the explanation of substance and accidents, terms which they have probably never used in any other context, and which may not be completely explained to them anyway, and they say it sounds like some sort of hocus-pocus and they aren’t going to believe it.
It’s a lot like if you went to an average 7th-grade chemistry student and tried to explain the truth about the “path” of an electron. Not only would they probably not understand it very well (and here I am not being insulting, because for sure I don’t understand it myself), but they might think it sounds like some sort of hocus-pocus.
However, people are more accustomed in our society to expecting science to be complicated, and something that requires learning to understand. But a lot of people expect faith to be “simple” by which they don’t mean that their faith itself should be simple (meaning that it is pure and untinged with doubt), but that the contents of faith should be simple. They feel that, despite the fact that God is so much greater than we are, all the things you need to know about Him should be understandable by a 7th-grader. They don’t realize that they need to have an educational preparation for understanding the concepts of substance and accidents, in the same way that they need an educational preparation for understanding the behavior of an electron.
They may also say that the average Catholic of, say AD 1250, wouldn’t understand the stuff about substance and accidents, either. This is obviously true. But the average Catholic in 1250 was probably spending a lot more of his daily effort just trying to keep his family alive, and was content to believe because he was told to believe by someone whose authority he trusted. This is NOT to imply that he was stupid, just that he did not have the leisure for intellectual curiosity that we (usually through no merit of our own) tend to have now.
So what we have now are people who are not content to believe because they are told by a reliable authority, but who nevertheless are not willing (or rather, do not see the need) to put the intellectual effort into understanding the things that need to be understood. And in addition, unlike the periodic table, the Real Presence is supernatural, and although greater understanding is possible (and desirable), complete understanding is NOT possible this side the grave.
So what people need to do is either decide to believe because of the words of Jesus and the 2000-year teaching of the Church, or to try to learn more about theology and come to a greater understanding that way. (Or the best way, IMO–do both.) Both ways require the constant support of prayer for faith. Prayer is the way the people who understand the Real Presence the best (the saints) came to at least some of their knowledge.
Unfortunately, what we are plagued with much more than the problems above is the “doubt of emotion.” This is what is happening when we say to ourselves, “I just don’t feel like that can possibly be the Body, Blood, Soul, and Divinity of our Lord Jesus Christ.” Frankly, there are only two useful things that can be done with this kind of feeling. First, pray against it. And, since we are not guaranteed to be able to “feel” properly about the things of God (we being fallen), the second thing that can usefully be done is purposefully to ignore it. Set it aside. Let it go. Realize that it doesn’t say as much about the state of the universe, or even the state of your mind, as it says about your sleep habits and the state of your digestion.
I hope this is in some way helpful. It’s helped me to write it.
–Jen