During the conquest of Israel, God promised that the Israelites would have control over the inhabitants of the land. They were to drive them out, and were specifically commanded to make no covenant with them or their gods, lest they make Israel sin against God.
Although we have no need to copy Israel from a physical perspective, the spiritual implications are still the same. We should make no covenant with pagans or their gods, lest they teach us to sin against Him.
Sadly, a lot of us don't seem to have learned this vital lesson. In the 19th century, a movement began to "free science from Moses" by introducing a Godless philosophy to science. Science, a gift given to man by God for His glory, was usurped by unbelievers as a tool to attempt to disprove Him. A new creation myth (which is actually a collection of old ones with a modern scientific veneer) was invented in an effort to cast doubt on the Bible's account of origins. Today, Evolution and the like are popular creation myths within our culture. And many Christians are making a covenant with its god.
The result is that these same Christians, not keen to just fall down a slippery slope, actually like to grab a sled and ride it straight into the depths of Hell. To clarify, I am not saying that Creation-compromising Christians are necessarily unsaved. Creationism, though foundational to the Gospel, is not the Gospel itself. Nevertheless, if we start asking "did God really say..." (sound familiar?) about one thing, where do we draw the line? If we ask "did God really say he created in 6 days?", why can we not ask "did God really say death is the penalty for sin?" If we ask "did God really say all men were made from one blood?", why can we not ask "did God really say all men are equal?" If we ask "did God really say He created us male and female from the beginning?", why can we not ask "did God really say you shall not sleep with someone of the same sex?"
The list goes on and on and on until ultimately, many Theistic Evolutionists are willing to say the Bible itself is just bronze age man's best guess. Maybe Jesus wasn't even born of a virgin. Maybe He didn't really do all those miracles. Maybe, just maybe, He didn't really rise from the dead. After all, whereas science can't really prove Evolution over Creationism, we can say quite definitively that dead men do not get up on the third day. Basically, if you start making covenants with the god of atheism, he will teach you to think and live as atheists.