What does Matthew 23:1 mean?

Matthew has been reporting on Jesus' conversations and teaching in the temple for much of the previous two chapters (Matthew 21—22). Christ's main topic has been the spiritual corruption of Israel's religious leaders. That exposition has included several parables and taking questions from representatives of the various groups of religious rabbis and officials. In this passage, He begins describing even more forcibly the consequences for the failings of the scribes and Pharisees.

He is speaking both to the crowds gathered at the temple for the Passover celebration, as well as to His own disciples. Perhaps some of the religious leaders are continuing to listen to Jesus, as well, though they are not mentioned. It's possible they have left after being so thoroughly dismantled in debate (Mathew 22:46), or they might be lurking around and listening without interacting.