God is an exchange of love. Why is it a mystery? Because we can’t know it unless God reveals us. God is one substance and three persons. God is love. All three persons in the Trinity are the same divine substance:
- The Father (The Lover)
- Jesus Christ the Son (The Beloved)
- The Holy Spirit (The relationship between the Father and the Son)
The love between them is so strong that is is a person in itself.
This video also has a nice explanation of what it means to be “eternally begotten” and “consubstantial”. This is helpful for a study of the Creed.