Jesus reveals that Yahweh is 1 God in three persons. This truth confounds those who refuse to accept the witness of Jesus and the apostles.
Father, Son, and Holy Spirit are revealed as one God, but each as a separate “person”. They are the same nature, the same being, who reveals himself or manifests himself to humanity by three distinct personages. This is the only way that the things Jesus taught can be true (as well as the teachings of prophets before Him, and the Apostles whom He sent).
Jesus was, before His incarnation, the Logos (or Word) of God – who was repeatedly revealed in earlier scripture. He is the one who met Abraham and Sarah. He remained distinct from other people and from the Father in Heaven. However, in Old Testament times the Holy Spirit came upon people and “annointed” them. This bonded with them in His presence of empowerment. Thus Kings and Priests were covered and blessed by the power of the Presence of Holy Spirit who came upon them and operated as an empowering guide or presence.
In the Apostolic time, the Holy Spirit came within the Apostles and the saints (believers) – so that now a person may become indwelt and permanently sealed by the Holy Spirit.
All are God, one God, in perfect unity of purpose and nature. Yet distinct in their personage, their method of interaction with mankind. While the Holy Spirit is here on earth, operating through His people by faith, Jesus and the Father remain in Heaven. This will once again change when Christ returns to the earth. The Holy Spirit’s presence will once again leave and return to Heaven while Jesus rules and reigns physically here – until the Father remakes the whole creation anew.