Deuteronomy 29:18
Lest there should be among you man, or woman, or family, or tribe, whose heart turneth away this day from the LORD our God, to go and serve the gods of these nations; lest there should be among you a root that beareth gall and wormwood;
The warning is that among Israel there could be on that very day a man or a woman or a family or a tribe whose heart turns away from the Lord God to go and serve the gods of the surrounding nations. Such a turning one becomes a root bearing gall and wormwood, producing bitterness and poison from within the community. The covenant warning binds both those present at the time and those not yet present. No one who follows a stubborn heart can presume to be at peace, because that apostasy brings God's curse and judgment.
A minister who preaches without the anointing of heaven enacts this root image by planting seeds in hearers that strike deep fibrous roots and spring up to bear poisonous fruit. Shepherds who profess to feed the flock leave them starving for the bread of life when they offer long discourses of anecdotes and cheap fodder, destitute of heavenly dew and rain, that move the feelings to tears without touching and breaking the heart. To strike in anywhere in a haphazard way or to talk politics mingles common fire with the sacred and dishonors God, showing no real evidence from God that the speaker is speaking truth. To sow uncertain ideas without knowing their source does hearers a grievous wrong.