Did you know that someone could depart from, turn away or abandon the faith? Paul is warning Timothy to be aware that this turning away, will happen in the church.

Some depart from the faith, the teachings or doctrine of Jesus, why? They have removed something that was the focus of their life & replaced it, they gave heed to something else. 

So how do people fall away, depart from the faith? Something deceptive comes along, it looks really good & they begin to follow it. They choose doctrines of demons over Jesus.