Adam Clarke on Ezekiel 3:20

When a righteous man doth turn from his righteousness - Which these words plainly state he may do, and commit iniquity and die in his sin; and consequently die eternally, which is also here granted; if he have not been warned, though he die in his sin, the blood - the life and salvation, of this person also will God require at the watchman's hand. Pastor hunc occidit, quia eum tacendo morti tradidit. "This man the pastor kills; for in being silent, he delivers him over to death." - Gregory. From these passages we see that a righteous man may fall from grace, and perish everlastingly. Should it be said that it means the self-righteous, I reply, this is absurd; for self-righteousness is a fall itself, and the sooner a man falls from it the better for himself. Real, genuine righteousness of heart and life is that which is meant. Let him that standeth take heed lest he fall.

And I lay a stumbling-block before him - That is, I permit him to be tried, and he fall in the trial. God is repeatedly represented as doing things which he only permits to be done. He lays a stumbling-block, i.e., he permits one to be laid.