Theology and "Irreparable Differences"

The sermon today at the church that I will soon be leaving was held by a guest speaker. The man, an Asian, humourous fellow, professed his belief in Calvinism. While prefacing his sermon with the fact that he is not necessarily right on everything, and that church members should follow the teachings of their individual churches (?), he did offer a staunch defense, armed with passages from the Bible and quotes from well-known Christians. The main argument of his was that predestination is real, and that God elects people who, when hearing the word of God, would come to accept it (while all others would not). He also said that it is impossible to know one is actually saved until Jesus returns or he or she leaves this Earth. Other arguments essentially defended Calvinism, mythbusting the rebuttals that claim that Calvinism makes evangelism or whatnot worthless.

Of course, this angered some people. Clearly, if this is true, it would be natural for some people to develop a dislike for God, as the preacher seemed to allude to the fact that God picked people to perish (the verses in scripture supported this). It also makes no reference to The Fall... did God know that was coming? Logically, the answer would be yes. But it doesn't seem that way.

Anyway, I'm not here to argue about Calvinism against Arminianism. My question is, while theologically, there are complete opposites, and really have a profound effect on our world... does it really matter to us at this point? It's good to be knowledgeable (and I am happy to see the sermon come up... honestly, it's appalling to see how many people don't realize that the church we attend believes in predestination)... but should it change the way we act?

Both still promote the Ten Commandments. Honestly, I don't think our behavior should change, regardless of what we believe. And I think that one does not need to know the correct theology (as if that wasn't hard enough) to be a Christian.

So yes. It was a great sermon, and it opened the eyes of many. But we have to remember... it's not everything.