It is useless for a man to flaunt his knowledge of the law if he undermines its teaching by his action.
One of the challenges the world has with Christians is when we don't live what we preach. As sinners, we will always fail. Don't allow your failures to become habits. Strive to be the best version of yourself to provide an example of Christ through your actions.
To the pure, all things are pure, but to those who are corrupted and do not believe, nothing is pure. In fact, both their minds and consciences are corrupted. They claim to know God, but by their actions they deny him. They are detestable, disobedient and unfit for doing anything good.