If a man is righteous and does what is just and right— if he does not eat upon the mountains or lift up his eyes to the idols of the house of Israel, does not defile his neighbor's wife or approach a woman in her time of menstrual impurity...
Ezekiel 18:5-6

"Eat upon the mountains" is a reference to participating in pagan sacrifices at the high places that God commanded Israel to destroy. Don't honor false gods through trees, mountains, or any other natural phenomenon. YHWH is the Creator and Master of them all, and he is particular about how he is to be worshiped.