"Trinity" was officially defined at Nicaea, but that did NOT mean that the early Christians didn't believe that Jesus wasn't the Lord.
The Trinitarian doctrine is based fully in scripture, nothing has been added.
Jesus was not of this world, that is why He had a virgin birth.
Jesus said He was a heavenly King, and one with the Father.
The Holy Spirit is not an angel or a man, but the very Spirit of God, of the essence and nature of God.
And this was believed by the Judeo-Christians, even modern Jewish-Chritiasn believe that Jesus and the Spirit are at one with God, the Father being the Godhead.