We all, in our lifetimes, have performed certain actions or deeds that God didn't like. When we gave our lives to Christ we asked for Him to purify our hearts. Because we are human, we might have kept ‘just a few’ habits–the use of some words, that shortness of temper, the saying of things ‘out of school’ about others.
Guess what? While these habits aren't evil–no one loses his or her life because of them, these tendencies displease God. He tells us here to get rid of them. He has a reason for saying this.
God’s desire is to have us live close to Him. He is so holy, He can’'t look on sin or anything displeasing to Him. While we realize that no one is perfect, He wants us to strive for that state.