Why can our oneness with Christ only be understood by faith?
Our oneness with Christ is a spiritual union, not a physical one, so it cannot be grasped by human senses or reason alone. Scripture reveals that believers, though separate entities, become one with Him, and God expects us to believe this revelation by faith.
Les explains from Ephesians 5 that Paul uses marriage to picture Christ's relationship to the Body of Christ. A husband and wife are two people, yet they become one; wedding ceremonies often illustrate this with two candles blown out and one lit. In the same way, believers and Christ are two separate entities, but once we enter into union with Him, we become one with Him. This is a deep concept, because it is entirely in the spiritual realm, and the only way we can comprehend it is by faith. The Book teaches it, so we must believe it; that is what God expects. Les also points back to Deuteronomy 29:29: the secret things belong to the Lord our God, but once they are revealed, they belong to us and our children forever. God is revealing this relationship between Christ and believers as members of His body.