This lamentation/complaint against Israel's wickedness and their practices of sacrifice is interesting because it is not only found in Isaiah 66 (the last chapter) but also in Isaiah 1:
3 The ox knoweth his owner, and the ass his master's crib: but Israel
doth not know, my people doth not consider.
4 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.
5 Why should ye be stricken any more? ye will revolt more and more:
the whole head is sick, and the whole heart faint.
6 From the sole of the foot even unto the head there is no soundness
in it; but wounds, and bruises, and putrifying sores: they have not
been closed, neither bound up, neither mollified with ointment.
7 Your country is desolate, your cities are burned with fire: your
land, strangers devour it in your presence, and it is desolate, as
overthrown by strangers.
8 And the daughter of Zion is left as a cottage in a vineyard, as a
lodge in a garden of cucumbers, as a besieged city.
9 Except the Lord of hosts had left unto us a very small remnant, we
should have been as Sodom, and we should have been like unto Gomorrah.
10 Hear the word of the Lord, ye rulers of Sodom; give ear unto the
law of our God, ye people of Gomorrah.
11 To what purpose is the multitude of your sacrifices unto me? saith
the Lord: I am full of the burnt offerings of rams, and the fat of fed
beasts; and I delight not in the blood of bullocks, or of lambs, or of
he goats.
12 When ye come to appear before me, who hath required this at your
hand, to tread my courts?
13 Bring no more vain oblations; incense is an abomination unto me;
the new moons and sabbaths, the calling of assemblies, I cannot away
with; it is iniquity, even the solemn meeting.
14 Your new moons and your appointed feasts my soul hateth: they are a
trouble unto me; I am weary to bear them.
15 And when ye spread forth your hands, I will hide mine eyes from
you: yea, when ye make many prayers, I will not hear: your hands are
full of blood.
16 Wash you, make you clean; put away the evil of your doings from
before mine eyes; cease to do evil;
17 Learn to do well; seek judgment, relieve the oppressed, judge the
fatherless, plead for the widow.
18 Come now, and let us reason together, saith the Lord: though your
sins be as scarlet, they shall be as white as snow; though they be red
like crimson, they shall be as wool.
19 If ye be willing and obedient, ye shall eat the good of the land:
20 But if ye refuse and rebel, ye shall be devoured with the sword:
for the mouth of the Lord hath spoken it.
This is consistent with Paul's declaration in Galatians 3 that the Law of Moses was intended as a "schoolmaster to bring us unto Christ". The sacrifices themselves had no innate cleansing power; their virtue was in the act of obedience to God's will, and in pointing their hearts towards the true sacrifice that they prefigured, the Atonement of Jesus Christ. If Israel forgot about that, when it was the entire point of the law, no wonder the Lord was annoyed with them!
