isaiah 66:3 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. - Free Bible Online

      3. God loathes even the sacrifices of the wicked (Isa 1:11; Pr 15:8; 28:9).
      is as if--LOWTH not so well omits these words: "He that killeth an ox (presently after) murders a man" (as in Eze 23:39). But the omission in the Hebrew of "is as if"--increases the force of the comparison. Human victims were often offered by the heathen.
      dog's neck--an abomination according to the Jewish law (De 23:18); perhaps made so, because dogs were venerated in Egypt. He does not honor this abomination by using the word "sacrifice," but uses the degrading term, "cut off a dog's neck" (Ex 13:13; 34:20). Dogs as unclean are associated with swine (Mt 7:6; 2Pe 2:22).
      oblation--unbloody: in antithesis to "swine's blood" (Isa 65:4).
      burneth--Hebrew, "he who offereth as a memorial oblation" (Le 2:2).
      they have chosen--opposed to the two first clauses of Isa 66:4: "as they have chosen their own ways, &c., so I will choose their delusions.

JFB.