"Every plant which My heavenly Father has not planted will be uprooted" (Matt. 15:13). Since the seed is the word of God (Luke 8:11), it is reasonable to conclude that "every plant" has reference to teaching and doctrine in general. Those plants that originated from God's seed (i.e., His word) would thrive, but those plants that grew from man's seed (i.e., human traditions) would be pulled up. Thus, any doctrine or teaching (or any "church" based upon such) that originates from man will ultimately be destroyed.
Jesus instructed His disciples to leave them (i.e., the scribes and Pharisees) alone (Matt. 15:14). Ultimately, every error will be dealt with by God (cf. Psa. 37:1,2). Jesus and His apostles did not (and we should not) waste time with men like this to the neglect of the multitude. We will have encounters with false teachers and we must "contend earnestly for the faith" (Jude 3) as well as mark those who need to be marked (cf. Rom. 16:17,18), but to become obsessed with dealing with these situations will cause us to miss opportunities to save others. Let us strive to influence those whom we can for good.
"They are blind leaders of the blind. And if the blind leads the blind, both will fall into a ditch" (Matt. 15:14). If a man knows that he is blind and allows another blind man to lead him, then he deserves to fall into the ditch. He should choose a suitable guide (cf. Psa. 119:105). The word of God must be our pillar of cloud by day and pillar of fire by night; we must move where it moves and stop where it stops. The implications of this verse definitely have the final judgment in view and perhaps also the destruction of Jerusalem where God uprooted their system of tradition. The scribes and Pharisees were not suitable leaders, but they didn't even realize they were blind!
Peter asks Jesus in Matthew 15:15 to explain "this parable." Jesus' words were like a parable to the disciples because they had difficulty understanding them. He seemed to be telling them just the opposite of what they had previously understood.
"Are you also still without understanding?" (Matt. 15:16). It was to be expected that the multitude, swayed by the teaching of the religious leaders, would be slow to grasp what Jesus said about uncleanness. However, his disciples, having been with Him for so long and having felt free to eat with unwashed hands, should have had better understanding.
Jesus explains that those things that enter one's mouth enter the stomach and are then eliminated. All foods are essentially pure and no food is defiled in and of itself (cf. Mark 7:18,19). The defilement comes when a person disobeys God in eating a food that He has prohibited.
Jesus continued in Mark 7:20-23 - "What comes out of a man, that defiles a man. For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, thefts, covetousness, wickedness, deceit, lewdness, an evil eye, blasphemy, pride, foolishness. All these evil things come from within and defile a man."
Spiritual defilement always originates from within. If a person has a pure heart and does not allow evil thoughts to harbor in his mind (cf. Phil. 4:8), then he will not be impure from any of the things Jesus lists here. Sexual immorality will never take place unless lust is first allowed to roam unbridled in the mind. Murder will never be committed unless one allows his hatred to conceive a plan in his mind. Stealing will not be a problem for the one who does not allow his heart to be afflicted with covetousness. All of the sins mentioned defile a person if that individual allows such wickedness to live in their heart. And when one allows this to happen, it will eventually be manifested in a physical act (cf. Matt. 12:34ff; Prov. 4:23).
These evil things that come from within not only defile a man but grow more vile with use (much like stirring up sediment in a body of water increases its darkness). Every obscene word a man speaks, every immoral story he tells as a joke, every angry word and oath he utters, and all the other things Jesus mentions here, clearly demonstrate what kind of character a person has.