“He answered, "Every plant that my heavenly Father has not planted will be rooted up.” Matthew 15:13
Concerning what plant exactly is this referring to? A biological plant, the Word of God (seed Matthew 13) or both?
It is a metaphor, so as a metaphor it does not directly relate to the actual thing said (namely, the biological plant), for all biological plants are planted and grow by God, the Creator of nature.
Then, what is that "plant" that is not planted by God if all biological plants are so planted? Surely, the non-biological "plants". But what are those non-biological plants not planted by God? It is tempting to say that evil and hypocritical teachers, the Sadducees and Pharisees, or all evil and deceitful men, who became evil by abusing their free will.
But it is blatantly wrong! For any man's being is fashioned by God and He sustains into being all, even the most evil of men being long-suffering to them, always willing them to repent. Thus all men are planted and sustained by God. But then what are those other "plants" not planted by God?
What remains is the evil deeds and choices of men, for they are indeed the "plants" not planted by God, and those "plants" lack ontological ground, for evil is deviation from the fullness of being, and as a deviation it is a non-being or quasi-being, and it will be sooner or later discovered and understood as such by an evildoer, and if he will have enough courage and faith in the all-merciful Lord, then he will repent and submit those sinful deeds and words to the consuming fire of the divine Mercy and Compassion (Hebrews 12:29), for only the good has ontological grounding and eternal future, whereas all evil as non-being will perish. God wishes to burn not men, created in His image and likeness, but the infection of evil in them through their responsive co-action and repentance, that is why also the Psalmist says "the way of the wicked will perish" (Psalm 1:4-6), - he does not say "the wicked will perish", but that the "way of the wicked will perish" so that the wicked may repent and turn away from this perishable way.
However, repentance is not automatic and necessary, depending on a sinner's free will and initiative, otherwise he runs a danger of falling out eternally from the Kingdom of Heaven, and eternally identify himself with those plants not planted by God, that is to say, his own sinful deeds, words and decisions - the non-realities; and this is what the eternal torment of hell means.