Jamieson, Fausset and Brown on Ezekiel 3:20

20. righteous ... turn from ... righteousness--not one "righteous" as to the root and spirit of regeneration (Psa 89:33; 138:8; Is 26:12; 27:3; Joh 10:28; Php 1:6), but as to its outward appearance and performances. So the "righteous" (Pr 18:17; Mt 9:13). As in Eze 3:19 the minister is required to lead the wicked to good, so in Eze 3:20 he is to confirm the well-disposed in their duty.

commit iniquity--that is, give himself up wholly to it (1Jo 3:8, 9), for even the best often fall, but not wilfully and habitually.

I lay a stumbling-block--not that God tempts to sin (Jas 1:13, 14), but God gives men over to judicial blindness, and to their own corruptions (Psa 9:16, 17; 94:23) when they "like not to retain God in their knowledge" (Ro 1:24, 26); just as, on the contrary, God makes "the way of the righteous plain" (Pr 4:11, 12; 15:19), so that they do "not stumble." Calvin refers "stumbling-block" not to the guilt, but to its punishment; "I bring ruin on him." The former is best. Ahab, after a kind of righteousness (1Ki 21:27-29), relapsed and consulted lying spirits in false prophets; so God permitted one of these to be his "stumbling-block," both to sin and its corresponding punishment (1Ki 22:21-23).

his blood will I require--(He 13:17).