"A pupil is not above his teacher; but everyone, after he has been fully trained, will be like his teacher (Luke 6:40)."
We usually quote this to point out how we need to be like Christ, imitating his actions and attitudes. While the Bible tells us we need to be conformed to the image of our Lord (Rom 8:29; 2 Cor 3:18; Gal 4:19), that is not the point Jesus is making here.
With a twist of irony, Jesus is talking about the dangers of blindness. If you follow a blind leader, you will fall with him into a pit. A person with a beam in his eye is too blind to a help to anyone. Sandwiched in the middle of these is the saying about a disciple being like his teacher.
How true. If he idolizes someone, he will start to talk like, walk like, dress like, and think like that celebrity. If a person's passion is to run with a particular crowd, he will eventually start to act, think, and dress like them. If you follow a person too arrogant, foolish, or blind to understand the consequences of his choices, you will wind up like him.
So the warning is clear. Be careful who you listen to. Be careful who you follow. Be careful who you run with. We are supposed to be salt and light (Matt 5:14-16). We are to be a godly influence rather than those around us being an ungodly influence on us. This is a call for discernment, wisdom and resourcefulness in our everyday associations. Think about it.