The Lord is here speaking of his judgment upon sinners, who despise his ordinances, and corrupt and pollute them. Mingling ought with them they become a pollution; Exodus 20:25.
Related Commentaries of Isaiah 66:15
Isaiah 66:15-17
15 For, behold, the LORD will come with fire, and with his chariots like a whirlwind, to render his anger with fury, and his rebuke with flames of fire.
16 For by fire and by his sword will the LORD plead with all flesh: and the slain of the LORD shall be many.
17 They that sanctify themselves, and purify themselves in the gardens behindd one tree in the midst, eating swine's flesh, and the abomination, and the mouse, shall be consumed together, saith the LORD.