How can we rationalize the concept of one God, with the concept of the Trinity?

God is one: Traditional Christianity says that God is one, yet insists that there are three distinct Divine persons of Father, Son and Holy Spirit. When you have three persons who are all–knowing, all–powerful, and all–present it makes three Gods. New Christianity says that God is one (Mark 12:32, Isaiah 44:6, Zechariah 14:9). The one God (out of love and concern for the human race and the state of humanity at that time) took on a physical human conceived of the Divine and born of the virgin Mary. Within the human of Jesus was the Divine itself – His soul was divine. Throughout His lifetime Jesus gradually got rid of what was merely human and took on more and more of the Divine within Him until He made His human completely Divine. This means, God is one, within whom is the Divine Trinity, and He is the Lord God the Savior Jesus Christ (Matthew 28:18). Just as we all have a soul, a body and the actions of our life (and are one person) so it is with God. The Father, Son and Holy Spirit are names given for the soul, body and activity of the one God. One God, one divine person.

Further references: Mark 12:29, 30, Deut. 6:4, 5, Matt. 19:16, 17, Isaiah. 37: 20, Isaiah. 45:5, 6, Isaiah 44:8, Psalm 18:31, Isaiah. 45:14, 15, 21, 22, Isaiah. 43:11, Hosea. 13:4, Isaiah 44:6, Zech. 14:9

Daily Inspiration

"All the life a person has comes from the Lord by way of communities."

Arcana Coelestia 8794:3