“Violent” means “desperate”; “take” is “seize” [see Matt. 11.11-13]—that is to say, to take for one’s possession. Since the Pharisees use force to prevent men from entering the kingdom of heaven, those who would enter need to seize it by force.

Mat 11:12 And from the days of John the Baptist until now the kingdom of heaven suffereth violence, and the violent take it by force.