The title is a statement made by Immanuel-Christ-Jesus[I.C.J.] to His disciples in Matt.15:1-14. This Chapter is serious meat, for mature Believers; only. I.CC.J. identifies the #1Enemy, and their m. o., which was accurate 2015 yrs. ago, and now. Remember, I.C.J. came in the flesh to defeat Death - which is another name of Satan.
I.C.J. was confronted by Scribes and Pharisees who were complaining that the LORD's disciples were transgressing the traditions of the elders. I.C.J. ask why did they transgress the Commandment of GOD, by their tradition? This id the #1 tool in Satan's toolbox = Religion!
They had made the Commandment of GOD of none effect, by their tradition. Christ then called them "Hypocrites" = play-actors, pretenders, deceivers.
Defilement is what comes out of the mouth - because it comes from the heart[mind]. The Pharisees were offended at this defilement comment. Christ Commanded His disciples to "let them alone: they are blind[no vision, full of darkness] leaders of the blind.