Jesus didn't try to defend his authority. It would be amply demonstrated. In fact, he had already demonstrated it throughout his ministry by casting out demons, healing diseases, and speaking with the power and wisdom of God himself. If his opponents refused to believe, there was nothing he could do or say to change that ... except maybe die and be raised again. But, he still didn't back down at their petty little displays of their token authority. Rather than argue with them about authority, he challenged them back with a question that would stump them. His question demonstrated what they refused to believe. Jesus knew authority. Jesus spoke with authority. Jesus was authority, so he asked them to answer him. They couldn't. They were left with only the bitterest of plans ... they must kill him! Even then, as we know today, they didn't have the authority or power to pull off their mission! Praise God; Jesus is the one authority over us all!