How do we know if a prophet is true or false?

In 1 John 4:2-3, we learn that the fundamental test of a spirit or prophet is their confession regarding Jesus Christ. Specifically, every spirit that acknowledges Jesus Christ's incarnation—'that Christ has come in the flesh'—is of God, while those who do not affirm this truth are labeled as false teachers or antichrists. This biblical criterion is crucial because it encapsulates the core of the Gospel: Christ's full deity and humanity. A true prophet's message must align with the entirety of Christ's identity and work as documented in Scripture, reflecting the attributes of the one true God.