Many preachers will tell you that the responsibility of Christians is to "do right." It becomes how they live their Christian lives. To them, the way to please God is to live by a moral code. Not "looking like the world," and going to church dressed nice carrying a Bible brings pleasure to God.
But they're wrong, for two reasons.
If you look at the Bible as a whole, and not just random verses scattered throughout it, you'll find out that the theme of the book is the reconciliation of man to God. In the third chapter, man (by sinning) loses fellowship (friendly relationship) with God. The rest of the Bible is about man coming back into fellowship with God and ends with the bride of Christ living forever with him. The entire thing is about relationship, and that's what God wants.
When asked by the Pharisees what the most important command was, Jesus said, "love the Lord your God with all your heart." That's what Christianity is, a relationship. The entire point of God's involvement in human history is so he could bring us back to him. The first thing he demands is for us to love him.
The second reason deals with God's sacrifice. We deserve God's wrath, not just because we sin, but because we have no righteousness of ourselves. Isaiah says that our righteousness is like filthy rags, worth absolutely nothing. But, II Corinthians 5:21 says, "he made him to be sin who knew no sin, so that we might become the righteousness of God." Because of Christ's death, not only did he take our sin, but he gave us his righteousness. He gave us his good works to be our own.
If we try to live by a moral code, we will ultimately fail because we are sinners. But we don't have to be righteous, because we have Jesus' righteousness. We are free to live in a relationship and worship him. God has given us a gift that is beyond all human comprehension. Mike Donehey from Tenth Avenue North said, "We shouldn't live for God, we should live because of God."