15 “Beware of false prophets, who come to you in sheep’s clothing but inwardly are ravenous wolves. 16 You will recognize them by their fruits. Are grapes gathered from thornbushes, or figs from thistles? 17 So, every healthy tree bears good fruit, but the diseased tree bears bad fruit. 18 A healthy tree cannot bear bad fruit, nor can a diseased tree bear good fruit. 19 Every tree that does not bear good fruit is cut down and thrown into the fire. 20 Thus you will recognize them by their fruits.
In Matthew 7:13-14, Jesus teaches that the narrow gate of heaven leads to life. But the wide gate of hell leads to death. Then in vv. 15-20, Jesus warns against false prophets. Why does He warn against them? The reason is that the false prophets lead people into the wide gate of hell.
I remember visiting Bangkok, Thailand for the first time. We went to a night market located inside the “red light district” in Patpong. The red light district is a place full of nightclubs and girly bars. I saw salesmen standing outside the doors of the bars. They wore long sleeves and ties, looking decent.
But these salesmen were selling sex. I recall seeing one salesman holding up a signboard. On the signboard were written all kinds of sex acts with a price. The salesman announced the sex acts in a loud voice.
The false prophets are the salesmen at the wide gate of hell. They call on people to enter the easy way. In effect, they prevent people from entering the hard way. (Davies/Allison) That is why false prophets are dangerous!