This year, the Czech Academy Awards got a big bump in star power when American comedy legend Jim Carrey showed up unannounced. The crowd erupted in applause as he opened the ceremony with confetti and his signature smile. It was only after the show that the truth came out — it wasn’t Jim Carrey at all. Instead, a lookalike had pulled off an elaborate ruse, fooling the producers.

But Hollywood isn’t the only place where everyone is not who they seem. In Matthew 5, Jesus warned his followers of the same thing:

Beware of the false prophets, who come to you in sheep’s clothing, but inwardly are ravenous wolves. (Matthew 7:15, NASB)

Christ was offering a warning about a problem that would soon endanger the stability of the early church. Over the first few centuries of its existence, the newly formed faith would face countless battles over its beliefs about everything from the nature of God, to Christ himself, and what it meant to follow him. Heresies like Arianism, Modalism, or Gnosticism were fiercely debated and defeated as the early church leaders fought to establish a firm foundation of doctrine about what they believed, and why.

Now, like the faux-Jim Carrey, these false prophets weren’t always obvious. Often they came from within the church itself. While they looked and sounded like Christ-followers, subtle differences in their beliefs about God were more than enough to put them at a dangerous distance from the teachings of Christ.

This is why we believe it’s so imperative that every Christian devotes time and energy of their own, both individually and together with their community, to the exploration of what we believe and why. Doctrine forms the bedrock of our faith, and in order to keep that foundation solid, we must dedicate ourselves to deepening and preserving our understanding of it. Only then, along with the guidance of the Holy Spirit, will we be able to correctly judge which teachings are true, and which are merely “lookalikes.”