“THE SACRIFICE OF THE WICKED IS AN ABOMINATION TO THE LORD: but the prayer of the upright is his delight.” Proverbs 15:8
The key to understanding the 66th Chapter of Isaiah is the proverb above and knowing that the prophet Isaiah was prophesying to a sinful nation.
“Ah sinful nation, a people laden with iniquity, a seed of evildoers, children that are corrupters: they have forsaken the LORD, they have provoked the Holy One of Israel unto anger, they are gone away backward.” Isaiah 1:4
THE WICKED JEWS SACRIFICED “clean animals”
The wicked Jews sacrificed “clean animals” such as the ox and the lamb --but those sacrifices were an abomination to the LORD because of their disobedience.
“He that killeth an ox is as if he slew a man; he that sacrificeth a lamb, as if he cut off a dog's neck; he that offereth an oblation, as if he offered swine's blood; he that burneth incense, as if he blessed an idol. Yea, they have chosen their own ways, and their soul delighteth in their abominations.” Isaiah 66:3
Many deceived people are using the following verse to condemn other Christians because they eat swine’s flesh:
“They that sanctify themselves, and purify themselves in the gardens behind one tree in the midst, eating swine's flesh, and the abomination, and the mouse, shall be consumed together, saith the LORD.” Isaiah 66:17
That verse refers to eating the sacrifices of the wicked. The wicked heathen of Isaiah’s day sacrificed “unclean” swine and the mouse in their idolatrous rites.
CONCLUSION: The wicked JEWS who sacrificed and ate “clean animals” and the wicked PAGANS who sacrificed and ate “unclean animals” are all an abomination to God. They will be destroyed together.