How do we know that the doctrine of union with Christ is true?

Union with Christ is not merely an abstract idea; it is a fundamental biblical doctrine directly supported by Scripture. For instance, Romans 6:3-5 explains that believers are baptized into Christ and are spiritually united with Him in His death and resurrection. This means that His experiences become our experiences — His death signifies our death to sin, and His resurrection promises our new life. Moreover, 1 John 3:9 underscores this doctrine by stating that those born of God cannot continue to sin, as they are said to have God's seed within them, representing a profound transformation that occurs through this union.