马太福音第七章第15—23节耶稣说要防备假先知，说他们外面披着羊皮，里面却是残暴的狼。这说明小心假先知特别重要，因为这关系到基督徒们心灵的日常饮食。耶稣已经来了，凡不传讲耶稣的教导即主的福音的都是假先知，约翰二书说不要请这样的人来讲道。彼得一书也强调要讲神的“very words”，而不能只讲旧约的字句，因为哥林多后书说字句叫人死而精意(即圣灵）叫人活，也不能讲一些从世界来的道理和从人来的传统。

 林后3:6 他叫我们能承当这新约的执事．不是凭着字句、乃是凭着精意．因为那字句是叫人死、精意是叫人活。〔精意或作圣灵〕
who also made us sufficient as servants of a new covenant; not of the letter, but of the Spirit. For the letter kills, but the Spirit gives life.

太7:15 你们要防备假先知．他们到你们这里来、外面披着羊皮、里面却是残暴的狼。
"Beware of false prophets, who come to you in sheep's clothing, but inwardly are ravening wolves.

摘自约翰二书英文版：
Anyone who runs ahead and does not continue in the teaching of Christ does not have God; whoever continues in the teaching has both the Father and the Son. (2 John 1:9)
If anyone comes to you and does not bring this teaching, do not take them into your house or welcome them. (2 John 1:10）
Anyone who welcomes them shares in their wicked work. (2 John 1:11)
For such people are not serving our Lord Christ, but their own appetites. By smooth talk and flattery they deceive the minds of naive people. (Romans 16:18)