Jesus quoted Isaiah 56:7 and Jeremiah 7:11 to explain his actions. The quotation from Isaiah highlights the temple’s importance for Gentiles. The temple’s design included the Court of the Gentiles, a place meant to help Gentiles come and worship the God of Israel and become part of God’s people.
Jesus judged Israel’s leaders because they were preventing Gentiles from properly using this part of the temple. They had turned a place meant to be a house of prayer for all nations into a den of robbers through dishonest business and profiteering.