God would not allow Moses to see him directly (Exodus 33:18–20). Only Jesus has seen the Father, so he alone completely knows him and can tell us about him (John 3:32–35; 14:9–10).
but the one and only Son: The Son, who sees the Father, is himself God. The Son is not simply a messenger who knows something about God. John explicitly affirms Christ’s deity. Jesus shares the substance of God’s being.