It seems to be a mystery, yet this mystery has been unveiled in the Scriptures.
Let's take a look at a few Bible passages:
In Genesis 1:1, 2, 3,
"In the beginning God created the heaven and the earth. And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.
And God said, Let there be light: and there was light."
This is just the first three verses of the Bible, and it's already revealed to us three Personalities: God, Spirit of God and the Light (Jesus: The manifestation of the spoken Word).
The Trinity is simply Three Personalities considered as One. It's the divine union of the Father, the Son, and the Holy Spirit. And every human being carries this three-in-one nature in them, the Soul (representation of the Father), the Spirit (representation of the Holy Spirit), and the Body (representation of Christ). The Soul would always go back to it's Maker (the Father), the Spirit is the consciousness of God living in us, and the Body is the connection of Christ in us who feels and understands our Injuries and Infections caused by iniquities, and our Infirmities.
Now, people often ask if the Trinity God is One God.