What does Mark 12:8 mean?

The Jewish leaders have asked Jesus who gave Him authority to toss over the tables used by the money changers and merchants in the temple courtyard. Jesus responds with a parable that goes much deeper than their original question.

It's not a question of which earthly authority empowered Jesus. It's not even about which earthly authority gave the chief priests, scribes, and Jerusalem elders authority to hold their positions. All their authority is granted by God according to His instruction. The priests are to perform their duties according to the Mosaic law. The scribes are to explain what the law means. The elders are to apply the Law to day-to-day situations. But like the second son in Jesus' prior parable (Matthew 21:28–32), they promise to obey God and then don't.

Jesus has made the point that He is there to do His Father's will (John 6:38), up to and including dying on a cross (Mark 14:36). The issue isn't a matter of who grants the authority given to Jesus and the others but who is obeying that authority. We can't injure God directly. We can't physically harm Him or take from His glory and sovereignty. He is all-seeing, all-knowing, and all-powerful. Although we can refuse to acknowledge His majesty, we can't take away from it. We can injure His representatives. In the Old Testament, those who refused to respect God showed their disrespect by harming God's emissaries—His prophets. In the New Testament, they kill His Son.

The religious and civil leaders kill Jesus because they don't want to give up the corrupted version of Judaism which they created: one that gives them power and authority God never intended. They don't realize that by rejecting God's authority, they are also rejecting God's protection. Within forty years of this incident, Jerusalem will be destroyed, Judaism will be in exile, and God will give the job of serving and worshiping Him to others (Mark 12:9).