There's a lot of misinformation going around in the name of Christ lately, not the least of which is the idea that you can become a Christian without changing the way you behave. I'm not saying we earn salvation. We can't. Scripture is very clear. "It is a gift of God, not of works."
Too many people, sadly including clergy, think that faith is basically a "Get out of hell free" card you can carry in your pocket silently until you present it at the pearly gates. In reality, if that's the card you're carrying, it's not going to work. Faith is an action noun. What we believe affects our action. For those who don't understand this, I offer, in no particular order, why even though you are saved by grace, you should still sin less and help more.
The token sports metaphor
Imagine you play on a small local sports league and after years of being a Blue Devil you join the Saints. Does that automatically make you a perfect player? No. You will still have fouls and penalties and you'll miss chances to score. What you won't do it try to score for the other team. In fact, you will do your best to stop them from scoring.
When you change such a minor affiliation, your behavior changes. Your goal changes. Likewise, when we join the Church our focus changes. You don't keep playing like you're on the devil's team. Unless you really are.
What does it mean to believe
This may sound obvious, but I've met several people who thought believing in God was akin to believing in Bigfoot. Faith is more than conceding the existence of some vague unknown. We actually know a lot about God through the scripture. Believing in God is believing in a person. You have confidence not only that they exist, but that they can be trusted to behave in certain ways. When we say we believe in God, we mean that we believe in an omniscient, omnipresent, all-powerful, infinitely-just Creator who has kept amazing promises and offered up his own flesh and blood to balance the scales for our sins.
If you truly believe in that person and he's given you rules for living, can you possibly ignore them just because you aren't going to have to pay the eternal price for disobedience? Or are you going to try very hard to incorporate his wisdom into every aspect of your life? The ten commandments are the users manual for human life written by the guy who designed and built the whole system.
Relationships
Many of the same preachers who don't talk much about the rules talk a lot about your relationship with Jesus, ironically. I don't disagree that our relationship with our Lord is crucial, but it shouldn't make you feel better about sinning. It should make you feel worse. If Jesus is truly someone you love and respect, why would you want to embrace the things that caused him to suffer the betrayal of his friends, public mockery and a painful death?
Or even be the friend who just never does what his friends ask? I bet you know that person. The one who shows up to the potluck with empty hands and a full wallet who doesn't use a coaster and puts his feet up on the furniture even though you've asked him a hundred times not to. The one who shows up when there's cake, but not when there's work to do. Is that the person you want to be to God?
Your witness
One of the most important things God asks from us is to share his Good News with others. To show his love and faithfulness to the world. Basically, we're supposed to walk around with a big God jersey everywhere we go.
So everything we do affects the impression others have of God. What should we want people to think of our religion and our God? That it makes for selfish, mean, dishonest, lawless hooligans or that it makes for generous, kind, trustworthy, responsible neighbors? Even as society embraces godlessness, people still inherently know right and wrong for the most part. They still recognize vice.
When we embrace that vice through our words or actions, we fail to reflect God's holiness. We make Christianity look like more of the same junk they can get anywhere. We become graffiti on the temple.
The wages of sin is death
No, really. Death.
The Ten Commandments aren't random. They aren't abstract or spiritual. They aren't things God decided to punish the harshest because He, personally, didn't care for them.
They are all poisons with different speeds and methods of toxicity, but they will all lead to death and misery. There isn't room here to follow each to that bitter end, but the paths are not hard to find. Even covetousness, that popular American pastime, is dangerous to the mind, soul and body.
Children put everything in their mouths until someone teaches them what is food and what is "icky. Spit that out." God has given us the ultimate "icky" list. When we keep ingesting it we hurt ourselves, our loved ones, and our neighbors.
God said so
A lot of Christians go through different stages in their relationship with scripture. Personally, I am at a stage of fascination with the complex correctness of God's word. I am reveling in the many ways He kept promises and revealed truths to us. When my friends who are at different stages say, "Because God said so," I tend to ask, "why?" Not because I doubt God, but because I want to find out more aspects of His plan. I love to increase my understanding of God's word. I love to see how it holds up from different angles and how it speaks to people in different situations.
But, honestly, I know that, "God said so." really is a compete sentence. It's good enough. He saved us from sin, not for sin. The Bible tells us so.
