Of God and the Holy Trinity (1689 BCoF Ch2 Para3)

In this divine and infinite Being there are three subsistences, the Father, the Word or Son, and Holy Spirit,²⁷ of one substance, power, and eternity, each having the whole divine essence, yet the essence undivided:²⁸ the Father is of none, neither begotten nor proceeding; the Son is eternally begotten of the Father;²⁹ the Holy Spirit proceeding from the Father and the Son;³⁰ all infinite, without beginning, therefore but one God, who is not to be divided in nature and being, but distinguished by several peculiar relative properties and personal relations; which doctrine of the Trinity is the foundation of all our communion with God, and comfortable dependence on Him.

²⁷ 1 John 5:7; Matt. 28:19; 2 Cor. 13:14
²⁸ Exod. 3:14; John 14:11; I Cor. 8:6
²⁹ John 1:14,18
³⁰ John 15:26; Gal. 4:6