the scribes: See 1:22. This warning is similar to the one against the Pharisees and Herod in 8:15. The scribes violated the two greatest commandments (12:30–31). They broke the first commandment by not loving God and by seeking respect and praise for themselves instead of reserving it for God.
long robes: These were likely clothes worn by religious men. To receive greetings perhaps meant being called Rabbi (see Matthew 23:7). The chief seats were in the front of the synagogue facing the congregation.