This suject is part of what is called "the Mystery of the Trinity", which is expounded in the Athanasian Creed, is

"to be adoringly believed on earth and only known in Heaven". Hence an understanding of it cannot be obtained as long as a "Creed" is allowed to define an attitue for us. We can, however, set the "Creed" aside, and go to the Scriptures direct, to find out from the Old and New Testament what grounds there are or are not, for the idea that Christ was one of "three persons" existing co-equally and co-eternally as "One God".