What makes Christians so suspicious of teachers/teachings that are suppose to have come from God? Well, the fact is, God gives His people the command to watch out for those who claim to speak for Him but, in reality, only speak to benefit themselves at the expense of others promoting the idolatry of the world. Deut 13:1–18 warned ancient Israel to be on the watch for such false prophets, who would lead them astray. They were to test the prophets by their teachings and resolve to follow only the commands of the LORD and hold fast to their God (Deut 13:4).
In teaching about the kingdom, Jesus warns His disciples that those in the kingdom of God must also watch out for false prophets:
Watch out for false prophets. They come to you in sheep’s clothing, but inwardly they are ferocious wolves. 16 By their fruit you will recognize them. Do people pick grapes from thorn bushes, or figs from thistles? 17 Likewise every good tree bears good fruit, but a bad tree bears bad fruit. 18 A good tree cannot bear bad fruit, and a bad tree cannot bear good fruit. 19 Every tree that does not bear good fruit is cut down and thrown into the fire. 20 Thus, by their fruit you will recognize them (Matt 7:15–20).
False prophets are those who teach men to follow the world in its worship of humanity, according to their own purposes. Their teaching cannot bring about fruit in the kingdom, because only kingdom teaching will produce kingdom fruit! You cannot have teaching from the world accomplish God’s purpose. Only God’s teaching will accomplish God’s purpose in the lives of His people.
The fruit of kingdom teaching is true discipleship. Jesus warns His disciples about those who claim discipleship according to their words, Lord, Lord (Matt 7:21a), and their religious activity, didn’t we prophesy in your name, drive out demons, and perform miracles (Matt 7:22). However, Jesus reminds them that disciples will be judged on their relationship to their Lord (Matt 7:23) according to the will of the Father in heaven (Matt 7:21b), when He says:
21“Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven. 22 Many will say to me on that day, ‘Lord, Lord, did we not prophesy in your name, and in your name drive out demons and perform many miracles?’ 23 Then I will tell them plainly, ‘I never knew you. Away from me, you evildoers!’ (Matt 7:21-23)