One thing I hear quite frequently from Christians is that they don't see the origins debate as especially important. Why does it matter if the days in Genesis are 24 hour periods, or long, undefined periods? Why does it matter if the Earth is 6,000 years old or 4.5 billion? Why does it matter whether God used the Big Bang or not?
The first, and I would say the primary reason it should matter to us is because it mattered enough to God to tell us. Even if it was completely trivial, irrelevant to every other aspect of our lives, God didn't inspire this book for us to ignore it. His prophets didn't spill their blood for it to gather dust on our shelves. His servants' bodies were not burned to ashes so that we could shrug it off. Every word God gave to us matters enough to God that the blood, sweat, and tears, that were shed in order for us to have them were a noble sacrifice. What Genesis says should matter to us because it matters to God, and only one interpretation, in the end, can be correct. The rest, as offensive as this word is in our culture, are wrong.
But the other reason it should matter to us is that just as it matters enough to God that we believe it, it matters to Satan that we don't. Genesis is indisputably the most attacked book in the entire Bible. The origins issue, aside from the problem of evil (which, coincidentally, can be efficiently answered with a correct understanding of origins, but not so much with compromised positions), is one of the most asked questions in all of the unbelieving world. Getting Genesis right matters because the devil wants us to get it wrong.
One particularly interesting martial art is Capoeira. Capoeira, unlike most martial arts, is not so much designed for efficiency in combat so much as stealth in training. It originated in Brazil in the 16th century, when Africans were sold as slaves. Naturally, slave traders/owners did not want their slaves training in martial arts. If someone has motive to harm you, the last thing you want is to let them practice. But dance? This was not banned. Capoeira is designed to disguise some very deadly combat techniques, strong enough to break bones, and even kill, as elaborate dance moves.
The analogy to be drawn here is fairly obvious. When Evolution and the like are an explicit threat, such as when Charles Lyell said he planned to free science from Moses, or when Charles Darwin said Evolution makes the Bible as invalid as the writings of the Barbarians or Hindus, Christians naturally go on the defensive. But if they disguise their combat techniques as dance moves, so to speak, what will we do to stop them?
As Michael Ruse, an Evolutionist himself, once said, Evolution is a religion designed as "...a full-fledged alternative to Christianity". This is precisely why the origins debate matters. If the Church ignores it, and especially if we compromise with the devil's ideas, we give him power. Power to convince those weak in the faith to abandon it. Power to stop other people from taking it up. Power to convince even the faithful to stand aside, stay quiet, and let him have free reign.
Now, not every Christian has to take a stand for Genesis. It's important, as is the entire Bible, but as Scripture says, we are multiple parts of one body. The eyes are not the nose, the nose is not the mouth, the mouth is not the hands, the hands are not the feet. We each have our own ministries. For some, that may mean working for a primarily creation-oriented ministry, like Answers in Genesis, or Creation Ministries International. But others may be more inclined to reach out to Muslims, in which case you can set aside origins almost completely. But reaching a culture whose primary objections to Christianity relate, in some way, to the origins debate, requires a correct understanding of the origins debate. Otherwise, the devil can capitalise on your weakness.