I do not ask that you take them out of the world, but that you keep them from the evil.  They are not of the world, just as I am not of the world. Sanctify them in the truth; your word is truth. As you sent me into the world, so I have sent them into the world.  And for their sake I consecrate myself, that they also may be sanctified in truth.  (John 17:15-19)

In his final, extended prayer for his disciples, Jesus asks his Heavenly Father to sanctify them.  The complexity of this prayer is revealed by understanding that ‘sanctify’ translates the Greek verb ἁγιάζω (hagiazó), which means ‘to make holy’ but also has the plainer meaning ‘to set apart’.