Now, don't miss the big point. We have a Triune (Three) God, Father, Son, and Holy spirit. Where does the idea of Four really come from? Consider Jesus's words in John 17, especially verses 20 and 21, "I am not asking on behalf of them alone, but also on behalf of those who will believe in Me through their message, that all of them may be one, as You, Father, are in Me, and I am in You. May they also be in Us, so that the world may believe that You sent Me." This looks like Three: Father, Son, and Us. The Holy spirit is simply not mentioned this time. So, with the Spirit we have Four. However, this Tetragrammaton will not be complete for and in us in this life, even though Jesus has set it in stone through His death and resurrection.