Its all a play with words. The Father talks about his only begotten, and in whom God is pleased. The Son Jesus Christ says if you have seen him you have seen the Father, the Father and I are one. He Jesus will send us the Comforter, the Holy Spirit, to live in the believer, the new Temple our bodies. The Three are one each with an office for perfecting Gods salvation. If God never died as a man, then there would be no salvation, so one part of God had to become man and a man also, to represent and be the mediator for man.For God to be able to live in man Jesus would have to send himself back as the Holy Spirit which is also the Spirit of God.
God said in Genesis "Let "us" make man in "our" image and likeness.God is three,Father, Word and Holy Spirit, as one God hence why man is three. Spirit Soul and Body as one Man.