Prayer is not a monologue. It is address: an “I” speaking to a “thou,” and Jesus prayed that way all the time. He rose before dawn to pray (Mark 1:35). At Lazarus’s tomb He said, “Father, I thank thee that thou hast heard me” (John 11:41). In John 17 He lifts His eyes to heaven, asks the Father to glorify Him “with thine own self,” and speaks of the Father and Himself as “we” (John 17:5, 11). He counts the Father and Himself as two witnesses (John 8:17–18). On the cross He cries, “My God, my God, why hast thou forsaken me?” (Matt 27:46).

If the Son simply is the Father, these prayers are either theater or a man talking to himself. Saying “the human nature prayed” does not solve it, because natures do not pray; persons do. Someone is speaking, and someone else is listening. That is what Trinitarians mean by distinct persons.