While the previous two posts were more for entertainment than enlightenment, and more for enlightenment than instruction, there might be one or two further points worth making on the internal act of faith.
First, the idea of faith varying with the degree of thinking or of assenting you do is not at all what St. Thomas was getting at in the article I quoted. All he was trying to do was distinguish "to believe" from other acts of the human intellect such as "to know," "to opine," "to suspect," and "to doubt." "To believe" is simply the act of being certain that a thing is so (like "to know"), while also being unable to directly see that it is so (like "to opine," "to suspect," and "to doubt," to list them (per St. Thomas) in increasing order of uncertainty).
Note that this conception of belief is a purely human phenomenon, valid quite apart from any notion of specifically Christian belief. I might believe the car keys are in the kitchen, not through faith in Christ, but through faith in my wife.
It's important that our conception of belief be purely human in this sense. If it isn't, then we are forced to choose between two unacceptable alternatives: either only Christians are capable of the human act of belief; or the Christian act of belief is a thing utterly different from the "purely human" act of belief.
The first alternative is unacceptable for the obvious reason that it's clearly not true. Non-Christians believe all sorts of things, which is to say they have faith in all sorts of things, just as Christians believe all sorts of things unrelated to the Faith (such as the location of car keys).
The second alternative (which is where we wind up if you insist I'm begging the question on what belief is when I state that the first alternative is false) is unacceptable because it makes Christian faith an inhuman, divine imposition on human nature, and as we all know grace perfects nature, it never supplants it.
Okay, so inhuman impositions on human nature are bad, but how does a Christian act of belief being a thing utterly different from the "purely human" act of belief constitute an inhuman imposition on human nature? Well, sort of by definition, right? If the very act of Christian belief is completely unlike any other human act, then what makes it a human act? Where does it come from, so to speak? We not only cannot perform the act of Christian belief without God acting directly first (and not in the uncaused cause sense, but in the sense of an Actor affecting other actors, through Divine revelation), we cannot perform any act anything like Christian belief. Apart from Divine revelation, this alternative would have it, there really is no human capability for Christian belief. When you consider that this is the one necessary act for salvation, the idea that it is utterly unlike every other human act is untenable; Christian faith would be as much an imposition on human nature as photosynthesis.