The mountain in Matthew’s Gospel is never incidental. It is the place of revelation (the Sermon on the Mount, 5:1), of temptation (4:8), of transfiguration (17:1), and here, of prayer. The ascent recalls Moses going up Sinai to commune with God (Exodus 24:18), but with a critical difference: Moses ascended to receive the word of God from without; Jesus ascends to commune with the Father in a relationship of eternal, interior union. He is not receiving instruction — he is resting in the love that is proper to the Son.
Matthew specifies that Jesus prays alone (kata monon) — a detail of immense importance. Though Jesus is the eternal Word through whom all things were made (John 1:3), and though his human will is perfectly united to the divine will, he nevertheless prays — and prays alone, in the silence of the mountain. This is not performance. It is not instruction for the crowds. It is communion. The Son speaks to the Father in the privacy of that relationship which is the innermost life of the Trinity.