There are plenty of things which divide fellow believers from agreeing on what God's plans are for the world, what they have been, and what he is doing now. But before I delve into anything further, I should define what all Christians agree on.
Christians believe that Jesus Christ was God the Son, and that he died on the cross for the sins of the World. They have accepted the sacrifice of Jesus as atonement for their sin, and have placed their faith in God, the creator of the Heavens and the Earth. [ed: added ..the Son... per Caleb's comment]
After that, they have a hard time agreeing on things. And these are things that will affect the way you live, and your outlook on the world. Here's a short list: the importance of Israel, are the children of believers automatically saved, Creation/Evolution, end times prophecy, and more. All of these issues boil down to one item. Hermeneutics, a fancy way of saying biblical interpretation.
There are a great many people in the world, a great many Christians who think there are hidden messages in the Bible, that there are things hidden in between the lines, that there is a deeper knowledge contained within the Bible. Be very careful about reading between the lines Be very careful about taking speculation too far. Be very careful about which passages you take at face value and those which you don't. You might just end up supplanting God's message with your own message.
What should be taken at face value you ask... Almost everything. Only when you arrive at a clearly allegorical piece of scripture should you do otherwise. Look at passages in their context, both grammatically and within history, if you want to discover the full meaning of the Bible.
Now, you ask, how does this affect all of those things I talked about earlier? It starts right at Genesis 1. God said he created everything in 7 days. Literal days. At this point you have some options: Believe God, call God a liar, or allegorize Genesis 1. I believe God, and those who go with allegory are basing that decision on the current views of science and it's (poor) ability to recreate history.
What about Israel. Paul in Romans talks about Israel in Chapter 11. He is very clearly stating that God still has a plan for Israel that he will yet deliver them. I happen to think this is one of the most amazing things you can witness on the Global front about what God is doing in the world. In the last 60 years God has restored the nation of Israel, he has gathered them after 2,000 years of exile. And not just exile, but fragmentation. It's amazing that the Jews haven't simply been forgotten after 2000 years, that the still exist. You would have thought they would have simply been assimilated and forgotten. Ever heard the Philistines mentioned in the news today? What about the Hittites. Historians had almost written these people off as fictional nations within the Bible, until Archaeologists dug them up. God is working in the world today, on the global scene.
What about the End Times Prophecy? Much of that is in regards to the book of Revelation and what parts of that people claim are allegories. But there are other passages in Daniel, Ezekiel, Luke and Matthew. Clearly not allegories.
Many people like to "read between the lines" in the gospel. Saying such nonsenses as taxes are evil and wrong, government is against God, and so forth. Why do people say these things, which are just not biblical, but yet they attempt to defend on some half-baked biblical argument? It all comes back to their interpretation of scripture. Ultimately, it's a pride thing, a search for more knowledge than what the rest of us possess. That through long study of the Bible you can have access to truth which is almost visible, but isn't really noticeable. There is more than enough knowledge and depth and meaning in the bible without adding verses in between the lines. Without taking more meaning than is acceptable from the scripture itself. Because doing so is making yourself a God, and putting your brain between you and what God has told us. And don't listen to people who have replaced the Bible with their own interpretation, which has become something wholly else. Not only is it wrong, but it's dangerous.
I want to end with, it's ok to speculate about things that are around the edges of what God tells us. Just be sure you let everyone know you're speculating about things...
Also, make sure your hope is firmly planted in Jesus Christ. If you think any person or thing besides God is going to make life better for you, you're wrong.