Luke 6:45

The (intrinsically) good man produces what is good and honorable and moral out of the good treasure (stored) in his heart; and the (intrinsically) evil man produces what is wicked and depraved out of the evil (in his heart); for his mouth speaks from the overflow of his heart.  

Our hearts need to be protected to produce what is good according to the word of God.  It means we have to be careful about outside influences of what we hear and watch.  If something has gotten into our hearts that is a bad influence, pray to God to help get it out. Don’t tolerate anything in the heart that hinders the relationship with Jesus.