In the sermon, Aaron talked about Tertullian (a 2nd century church father). Tertullian explained the puzzle of the Trinity as such; In the Roman Empire, the Emperor shared power with his son, declaring him “co-emperor.” In these cases the empire itself was not divided… but each had full imperial authority over all the land. Each was emperor, each was in full possession of imperial power, and that power was not divided…yet one of them was not the other. Tertullian said, “Divinity is shared by the Father, the Son, and the Holy Spirit. There is only one divinity, only one God, just as there is only one empire.”
 

The Trinity teaches us that God, who is the ONLY God, does not stand alone in solitary splendor, God Himself exists in relationship. God is one, and yet God is one in community. If anyone ever says to you that the doctrine of the Trinity asks you to believe in the nonsensical notion that three can be one, we can answer that, on the contrary, the Trinity is a unique example of what it means truly to be ONE. God’s oneness is such that there is love even within the Godhead itself. God is love, not just in the sense that God loves us, but also in the sense that the inner life of the Trinity is a life of love.