The apostle John wanted the readers of his letters to clearly understand how they could identify the Spirit of God in the people they encountered.

When Jesus was still on the earth, He healed many people who were possessed with unclean, evil spirits (see Matthew 8:16, Luke 8:29, and Luke 11:14, for example). John saw this firsthand when he followed Jesus — though he never wrote about these healings in his gospel.

In John’s later writings — John I, II, and III — he warns against gullibility. “Beloved, don’t believe every spirit, but test the spirits, whether they are of God because many false prophets have gone out into the world,” he says (1 John 4:1). In other words, don’t believe everyone who claims to be a Christian.

With his own ears, John had heard even demons recognize Jesus’ divinity (Matthew 8:29). He had been present at Jesus’ crucifixion — he knew how easily people could be misled. So he presents those who come after him with a foolproof way of recognizing God’s Spirit in those they meet: “every spirit who confesses that Jesus Christ has come in the flesh is of God.”

We may quibble over different styles of worship, but we must never fail to recognize God’s Spirit in our brothers and sisters who, like us, claim Christ as God’s Son and their Savior.