William Burkitt on Matthew 23:15

The next woe denounced is for their false-ended zeal and earnestness in proselyting heathens to the Jewish religion; not with a pious intention to save them, but to serve themselves upon them, to have their consciences and purses under their power: and when you have poisoned them, says our Saviour, by your corrupt doctrine, and hardened them in a course of sin by your wicked example, they are more the children of hell than before you practised upon them.

Learn, 1. Great is the diligence and indefatigable the industry which false teachers use in gaining proselytes to their opinion and party: They compass sea and land to make one proselyte.

2. That such as are proselyted to error, are oftentimes faster riveted in their false opinions than their teachers themselves: They are made two-fold more the children of hell than yourselves.