Albert Barnes on Matthew 22:34

The Pharisees--were gathered together. That is, either to rejoice that their great rivals, the Sadducees, had been so completely silenced, or to lay a new plan for ensnaring him, or perhaps both. They would rejoice that the Sadducees had been confounded, but they would not be the less desirous to involve Jesus in difficulty. They therefore endeavoured, probably, to find the most difficult question in dispute among themselves, and proposed it to him to perplex him.