It would be wonderful if we would do what this verse says everyday! Trouble is, we're too content to let some of our fleshly habits "hang around" or we pick up other activities that we know are wrong, but we think we can "dabble" in them without getting infected by them! That's just foolish, Proverbs 14:9.
Paul is telling us to take the "old clothes" of our old nature and throw them off. Though we never get rid of the affects of our old nature during our earthly lives, we don't have to yield to the old nature's allurements and temptations. We have the power in Christ to say "No" to sin! And if we would look at our old life as disgustingly dirty as it is, then we should all the more desire to rid ourselves of its influence on us! Again, the trouble with many Christians is that we've gotten use to the odor and seem to be content to wear old, smelly clothing over a clean body! Remember, 1 John 1:9 makes clear that the Lord "cleanses us from all unrighteousness" every time we confess our sins. He cleans us! So why do we insist on putting the old clothes of our old nature back on?! Throw them back on the rag pile and leave them there!