That which we have seen and heard declare we unto you, that ye also may have fellowship with us: and truly our fellowship is with the Father, and with his Son Jesus Christ.
The early Christians, including John, believed in one God, the Father and one Lord, Jesus Christ.
If God was a Trinity this would be a great place to show it, but John did not believe in a Trinity. His fellowship was with the Father and with His Son. There is no mention of the Holy Spirit. Did he just forget the third person of the trinity?
The Holy Spirit is the indwelling power and presence of God. The Holy Spirit is God's Spirit and is the Spirit that joins us all. Through the Holy Spirit we have the indwelling presence of both the Father and the Son.
The truth is revealed to those who seek.
John 14:23 Jesus answered and said unto him, If a man love me, he will keep my words: and my Father will love him, and we will come unto him, and make our abode with him.
