Book 1 - Knowledge of God the Creator
Chapter 13 - One essence of God, which contains Three Persons
Sections 1-6 - Trinitarian terms used by the early church fathers
Section 1 God's nature is immeasurable and spiritual
The Manichees made evil equal with God, denying His infinity.
Others imagine a coporeal God, denying His spiritual nature.
God speaks sparingly of His essence, "to keep us sober."
We can't measure God by our own senses or mind.
In speaking of His own arm, hand, etc., God speaks with a "lisp,"
to accommodate our "slight capacity" to understand Him.
Section 2 - The three "Persons" in God
God reveals Himself in 3 persons so He will "be contemplated clearly."
The word hypostasis (person) comes from Hebrews 1:3.
It can't mean essence, since God's essence is indivisible.
The preceding phrase in Heb 1:3, "the brightness of His glory"
shows the 2 separate persons of Father and Son.
Section 3 - The expressions "Trinity" and "Person" aid the interpretation of Scripture and are therefore admissible
Some object that these terms aren't in Scripture
But the words help explain what is in Scripture.
The objection is valid to a point, as outside words can lead to undue speculation.
But using them sparingly, with Scripture staying the rule, is safe and beneficial.
Section 4 - Such terms are needed to unmask false teachers
They "cloak their errors in layers of verbiage."