WCF 2: Of God and of the Holy Trinity

2. God hath all life, glory, goodness, blessedness, in and of himself; and is alone in and unto himself all-sufficient, not standing in need of any creatures which he hath made, nor deriving any glory from them, but only manifesting his own glory in, by, unto, and upon them. He is the alone fountain of all being, of whom, through whom, and to whom are all things; and hath most sovereign dominion over them, to do by them, for them, or upon them whatsoever himself pleaseth. In his sight all things are open and manifest, his knowledge is infinite, infallible, and independent upon the creature, so as nothing is to him contingent, or uncertain. He is most holy in all his counsels, in all his works, and in all his commands. To him is due from angels and men, and every other creature, whatsoever worship, service, or obedience he is pleased to require of them.

3. In the unity of the Godhead there be three persons, of one substance, power, and eternity: God the Father, God the Son, and God the Holy Ghost: the Father is of none, neither begotten, nor proceeding; the Son is eternally begotten of the Father; the Holy Ghost eternally proceeding from the Father and the Son.

For additional study see:

1. WSC 4:  What is God?
2. WSC 5:  Are there more gods than one?
3. WSC 6:  How many persons are there in the Godhead?
4. WLC 7:  What is God?
5. WLC 8: Are there more Gods than one?
   
6. WLC 9: How many persons are there in the Godhead?
7. WLC 10: What are the personal properties of the three persons in the Godhead?
8. WLC 11: How does it appear that the Son and the Holy Ghost are God equal with the Father?