When we talk about "believing" in something in order to be saved, we always open the door to the question "then how much do you have to believe?" The thief on the cross gets a lot of press because he is a good example of "the minimum" (for lack of a better word) required to "get in." it seems he had little or no theological understanding of anything, much less the trinity or other deep topics. He simply submitted to Jesus as his Lord and Savior, based on the somewhat limited knowledge at his disposal, namely watching how Jesus was suffering and dying. Sure, he may have been fortunate enough to have heard Jesus teach at some point prior to being arrested for thievery, but this is not stated in scripture. Thank God you don't have to be a rocket scientist in order to be truly saved. I never did understand trigonometry.
Hey wait a minute-- trigonometry... trinity... is there some correlation here?