How do we know the messages given by prophets were about Christ?

The certainty that the messages of the prophets were about Christ is rooted in Scripture's teaching that the Spirit of Christ was active in them. As stated in 1 Peter 1:11, the prophets searched intently to understand the time and circumstances under which these messages would be fulfilled. The Spirit revealed to them that what they prophesied pointed beyond their own time to the coming Messiah—Jesus Christ. This connection is further seen in the fulfillment of prophecies concerning His birth, life, death, and resurrection, all of which affirm that the entire narrative of Scripture is centered around the person and work of Jesus. The narrative builds a comprehensive picture of God's redemptive plan, culminating in Christ, as He fulfills the law and the prophets, thus defining our understanding of the entire biblical story as one that leads to Him.