Comparative Advantage

In any market, the individuals who have comparative advantage strive. In trade, a comparative advantage in producing a good that others need puts you in a great position. You can find someone who needs your good who can't produce it as efficiently as you can and get something in return that will be beneficial for you. America has done so well over the past few centuries because they have maintained a comparative advantage in innovation. As long as you stay innovative, you will find more efficient ways of doing things, which in turn will lead to you being successful. Businesses are constantly searching for anything that will give them a leg up on the competition, or a comparative advantage. For example, if McDonald's can find a more efficient way of making cheeseburgers than Burger King can, then they will likely be more successful than Burger King. In Civ, it is important to constantly upgrade technology and remain innovative to stay ahead of the rest of the market. If new technology enables you to grow crops more efficiently, then you will produce more food and be able to feed a larger population. If you can do things more efficiently than the rest of the market, then you will be successful.

Religion

I am a religious person, but at the same time, I feel that leaders of many civilizations over time have altered their religions to better control their followers. In the days of feudalism, the economy was run by tradition. That is, if your father was a serf, then you were a serf. There was no central government with a code of laws keeping people in line. The only form of authority were lords, who governed their manors. There was, however, religion, which kept people in line. The church was very powerful, and Christianity was the main religion, which was based around morals. It is convenient that the religion of that time was based around morals, because it was a way for the authorities to "brainwash" their followers into conformity. Not to say that Christianity is wrong, because I am a Christian myself, but it did help those who were in charge.
Similarly, in the time of Moses, Moses convinced his people that God wanted him to deliver them from the evil Egyptians. He gained the support of his followers by telling them that it was right according to their religion. Eventually, people turned on him because they were skeptical of the truth of his words. God may actually have gone to Moses to and told him to deliver his people to freedom. It was again convenient for Moses to use religion as an argument, though. So, religion is perhaps the best way to ensure conformity from your followers. Even today, there would likely be far more crimes and hostile people were it not for religion.
In the game, I chose to advance my religion at every opportunity I had. I feel that this made my civilization more unified, just as religion does in real life. Without religion, there is no force that is above all else to provide a set of guidelines and a common set of beliefs for your people.