Isaiah 66:17,18

They that sanctify themselves— These verses specify the cause of the extreme severity denounced in those preceding, and are to be understood figuratively, like the expressions used in Isaiah 66:3 and in ch. Isaiah 65:3; Isaiah 65:11. אחד אחר achar achad, Behind one tree, may be rendered, After Hecate, or Ahad, which Ahad, or Adad, was an Assyrian idol. See Selden, and Macrob. Saturn. 23. In the midst, may either signify publicly, without any fear or shame, (see ch. Isaiah 19:19 Isaiah 61:9.) or it may refer to the idol's being placed in the midst of the sacred grove.