Jesus, at the close of the Sermon on the Mount, speaks some of the most frightening words in all of Scripture. He draws a clean distinction between those who are saved and those who are deceived in thinking they are saved.
He begins by explaining the narrow way to life and the broad way that leads to destruction (Matt. 7:13-14). And many, He says, go the way of destruction.
He then tells us we will know those who are deceived by the lack of fruit in their lives. Spiritual fruit is the only evidence, according to Jesus, of true salvation (Matt. 7:15-20).
Finally Jesus tells us many will be deceived on the Day of Judgment and be cast from the Lord's presence. Why? Because they "practiced lawlessness" (Matt. 7:21-23).