People get all upset at the word "sin" but for a believer in Jesus Christ it's really no big deal. How can I make such a statement?
When sin keeps us away from God - it is a VERY big deal. After all God went to a lot of trouble to get us out from under it. For someone who has never made a commitment to believe in Jesus Christ for salvation - sin is a big deal. It is a wall between that person and the God who wants them to know Him.
Because I know God and He took care of all my sin when Jesus died on the cross and came back alive almost 2,000 years ago. Every day of our life we fail in different areas. Sometimes it is blatant and intentional and sometimes it's not intentional. Either way we hurt someone else, ourselves or God in some way -- a mean thought, an unkind word, a lack of thankfulness... But I can come to God, confess these things and know for sure I am one of my Father's favorite people. I don't have to earn His favor, He already gave it to me.
For those trying to earn their way to heaven sin is devastating because you have to start all over again and get back in good standing. But the Lord Jesus Christ did not go through what He did so I could try to earn my way to heaven. In fact, He knew I could never earn my way to heaven - that's why He did what He did.