It's just one little lie. What's the big deal? A lie cost Ananias and Sapphira their lives. They had sold their property and kept some of the money for themselves but when they came to give it to the apostles to help the needy, they lied about how much they had sold the property for thinking nobody knew what they had planned together. The only problem was they didn't think about the fact that God is all knowing and He sees everything! Peter calls them out on it and said, "You didn't lie to us...you lied to God!" Immediately they fell to the ground dead. It may seem unfair and extreme to us but it got the point across to the early church...God is serious about sin and we better be if we call ourselves a Christ follower!