for me Kant's only relevance here is his epistemologic approach, concerning the 'what can be understood' part.
but you can approach the question ontologically, just like Heidegger did. dasein's fundamental modes of being are being-in-the-world and having-a-world. in order to-have-a-world, dasein must understand it. can infinity be understood? what I want to emphasize here is that infinity is not present in my world, it's something out of it. or e.g. supernatural expresses this the most, since it almost literally tells that god is out of this world. so for my mode of being it is just as unreachable, as a 3 dimensional thing for a 2 dimensional being.
or there is Rorty, let's focus on our lives and use what is useful for us. do I need god for some reason? if yes, I believe in it, or to be more precise I believe in something what I want god to be like.. as Putnam says you can only refer to what you are conscious of. what do you refer to when you say infinity? (not to mention god.) by no means one can refer to it, only to a/his/her concept of it, which is necessarily vague.
etc, etc.
but from many these come something interesting, concerning the design argument. in trying to understand god, we are creating it in a way we can understand. it's just laughable.
