Then one of the experts in the law of Moses [Note: Matt. 22:34 identifies him as being a Pharisee also], came and heard Jesus and the Sadducees discussing together [i.e., the subject of the resurrection], and knowing that Jesus had refuted the Sadducees successfully, asked Him, "Which commandment is foremost, above all the others?"

Now John's disciples and the Pharisees were fasting, [i.e., going without food and/or drink for religious reasons]. Some people came and asked Jesus, "Why do John's disciples and the Pharisees' disciples fast, but your disciples do not?"

Then Jesus ordered them, saying, "Pay attention and watch out for the leavening [effect] of the Pharisees and Herod." [Note: By "Herod" is probably meant the Herodians, who were a party favorable to King Herod and, along with the Pharisees and Sadducees, were out to get Jesus. See Matt. 16:6].