Think of the Father as a spring of life begetting the Son like a river and the Holy Ghost like a sea, for the spring and the river and sea are all one nature. Think of the Father as a root, and of the Son as a branch, and the Spirit as a fruit, for the substance in these three is one. The Father is a sun with the Son as rays and the Holy Ghost as heat.

John of Damascus (Monk, 676 – 749)