'I ask for mercy and not sacrifice, and if you knew what this meant, you'd not condemn the innocent' is in reference to Hosea 6:6; where 'the knowledge of God is more important than your burnt offerings.'
It doesn't just apply to animals, the priests had been murdering the prophets 'lewdnessly' in Hosea 6:9.
Yeshua challenged the Sanhedrin for saying that the murdering of the prophets counted as atoning sacrifices in Matthew 23:27-38, Mark 7:1-13, and the Parable of the Wicked Husbandman (Matthew 21:33-46, Mark 12:1-12, Luke 20:9-19).
There are two references to 'I ask for mercy, and not sacrifice' (Matthew 9:13 + 12:7); where Yeshua tells us 'he doesn't come to call the righteous, yet the sinners to repentance.'
It was prophesied in the Parable of the Wicked Husbandmen, that the Pharisees would rewrite the Gospel to the Gentiles, by saying that through the death of the son they'd gain an inheritance, yet they'd be condemned by God for it at Judgement Day.
John, Saul, and Simon petros were Pharisaic, teaching Balaam teachings (Micah 6:5-8 - which is to say God required sacrifice), as they built their teachings on the oral tradition Yeshua challenged in Mark 7:1-13: "that the death of the righteous, can atone for the sins of that generation."
They'd turned that oral tradition into the belief, that by praying at the prophets graves, you could have your sins forgiven in Matthew 23:27-38, and thus Yeshua being the spirit of YHVH, cut them off two thousand years ago for defiling the law.
What you need to understand is that all of this was to fulfil prophecy, God knew 'the lying pens of the priests' would make up a new religion to snare the Gentiles, God foresaw that 'they'd use the Messiah as a snare to trap men', all of it was done to create the Bed of Adultery in Isaiah 28:9-19+20-21, yet most are not wise enough to see it.