Take a listen to this 6min episode from the seventh chapter of the Book of Mark in regard to what is it that defiles a man. The rulers in Jerusalem had already determined to kill Jesus (Jn 5:18). No doubt they heard of His waning popularity in Galilee (Jn 6:66). They now sent this delegation of Pharisees to push their propaganda campaign, hoping to make Him more unpopular with His own disciples, for it is likely that many of them held to the same traditions as the Pharisees.
The hand washing described in these verses was purely ceremonial and was not for sanitary purposes. It was not prescribed in the Law but was an invention of the teachers of the Law.
The Pharisees and the scribes were guilty of the sin of legalism. A legalist substitutes outward acts or words for proper inner attitudes that come from being born of God and the Spirit.
The righteousness of the scribes and Pharisees was external only as they kept many rules; they prayed, praised, fasted, read God's Word, and attended worship services. However, they substituted the outward act for the correct inner attitudes. Jesus said the righteousness that God requires of the believer is more. The heart and spirit, not only the outward deeds but must conform to God's will in faith and love.
The heart in Scripture is the totality of intellect, emotion, desire, and volition. Contemporary people generally consider the head with its brain to be the center and the director of human activity. However, the Bible speaks of the heart as the center; "out of it are the issues of life" (Prov. 4:23). Many other spiritual activities take place in the hearts of regenerated believers. They praise God from their heart (Ps. 9:1), meditate on God's Word continually in their heart (Ps. 19:14), cry out to God from the heart (Ps. 84:2), seek God with all their heart (Ps. 119:2,10), hide God's Word in their heart (Ps. 119:11), trust in the LORD with their whole heart (Prov. 3:5), experience the love of God poured out into their heart (Rom. 5:5), and sing to God from their heart (Eph. 5:19).
An impure heart will corrupt one's thoughts, feelings, words, and actions (Prov. 4:23). What is needed is a new, transformed heart, made after the image of Christ (see Luke 6:45). Therefore, it's not as the Word states, that which goes into a man that defiles him because what goes in enters the belly and exits out into the draught. In short, those awful actions, those mean things spoken from your lips are from within your heart. Think about it.