What do you do when a fellow believer is led astray by false teaching?

We live in a day and an age when “open-mindedness” is the motto, even in the church of Jesus Christ. Many people cannot quote John 3:16 but almost everyone can quote Matthew 7:1 (even if they do not know the reference). The problem with this mentality is that people are open to every form of teaching under the sun. Not everything that is spoken from a pulpit is from the Bible. Not everything that you see on a “Christian” television station is sound doctrine. We must learn to discern good teaching from heretical teaching. The thing about heretical teaching is that it is presented in a positive way and seems to be correct, especially if you do not have a firm grasp on the Scriptures.