How do we know that Christ came in the flesh?

The Apostle John, writing toward the end of his life, asserts the importance of the incarnation of Christ, stating, 'We know that the Son of God is come.' This declaration is crucial as it refutes heresies that denied the true human nature of Christ. Gnosticism, Dorsetism, and Sorinthianism were ideologies that questioned or denied the reality of Christ's incarnation. John's testimony as an eyewitness to Christ's life and work reinforces the assurance that Jesus was both fully God and fully man, which is vital for understanding His atoning work. Acknowledging Christ’s coming in the flesh is foundational to the Reformed faith, as it undergirds the doctrines of grace and salvation.