1 If any among you says that the Trinity indeed exists, then explain what exactly is this one God in three persons. What is the Holy Father? What is the Son? What is the Holy Spirit? Is Jehovah the Holy Father? Is Jesus the Son? Then what of the Holy Spirit? Is not the Father a Spirit? Is not the substance of the Son also a Spirit? Was not the work of Jesus the work of the Holy Spirit? Was not the work of Jehovah at the time carried out by a Spirit the same as Jesus’? How many Spirits can God have?
2 According to your explanation, the three persons of the Father, the Son, and the Holy Spirit are one; if so, there are three Spirits, but to have three Spirits means there are three Gods. This means that there is no one true God; how can this kind of God still have the inherent substance of God? If you accept that there is only one God, then how can He have a son and be a father? Are these not all simply your notions? There is only one God, only one person in this God, and only one Spirit of God, much as it is written down in the Bible that “There is only one Holy Spirit and only one God.”
3 Regardless of whether the Father and the Son of which you speak exist, there is only one God after all, and the substance of the Father, the Son, and the Holy Spirit you believe in is the substance of the Holy Spirit. In other words, God is a Spirit, but He is able to become flesh and live among men, as well as to be above all things. His Spirit is all-inclusive and omnipresent. He can simultaneously be in the flesh and throughout the universe. Since all people say that God is the only one true God, then there is a single God, divisible at will by none! God is only one Spirit, and only one person; and that is the Spirit of God.
Adapted from “Does the Trinity Exist?” in The Word Appears in the Flesh