I've been fairly busy lately, however I have been reading an article by Joseph Raz, "Reasons: Explanatory and Normative"in New Essays on the Explanation of Action (a link to this paper can also be found on his personal website). In this paper he makes an interesting comment on the rationality of belief. He says, "The rationality of believing depends on one's openness to critical evaluation of the belief, one's ability and willingness to revise or reject it were the evidence to point that way.(p. 189)"
It seems to me that he has a certain point, however, there is more to the rationality of a belief then the agents willingness to be open to a critical evaluation and potentially change his belief. It seems that more importantly a belief is rational when it is based upon valid reasoning, or, we could say, when it is logical. It also seems to me that a belief that is true is rational in the sense that it is rational to believe it, even if one did not arrive at that belief through a process of reasoning.
We need to make sure that when we say that we belief X (X is a place holder that is used to refer to any proposition) that we have a reason to believe X. In other words, we need to make sure that our beliefs are rational. This is what Peter says in 1 Peter 3:15 "But in your hearts honor Christ the Lord as holy, always being prepared to make a defense to anyone who asks you for a reason for the hope that is in you; yet do it with gentleness and respect." We need to make sure that it is rational to believe what we believe, and that our beliefs are rational.