Cazier divides the next sententia into two parts, 1.1.6a and 1.1.6b. I’m going to follow him here.
In this sententia Isidore draws the conclusion of divine simplicity:1
Ideo Deus dicitur simplex, sive non amittendo quod habet, seu quia non aliud est ipse et aliud quod in ipso est.
For that reason God is called simple, whether by not losing what he has, or because it is not the case that he himself is one thing and that which is in him another.
He tenders two possible justifications for the doctrine. The first has to do (again) with immutability: if God does not lose what he has, then he must be unchangeable, ever the same. John of Damascus again: “For all that is created is changeable, and only that which is un-created is unchangeable” (Exposition of the Orthodox Faith 2.3).
The second has to do with what was discussed last time: there is actually no difference between God and his attributes; they are identical.
I append two passages drawn from Gregory the Not Too Bad’s Moralia in Iob, referred to by the editors of the Patrologia Latina text (at least I think so: these are both from books mentioned in their notes, but not from the sections to which they refer. I have to imagine that either (1) the section-numbering in the edition they used was different, or (2) the references are imprecise; I’m pretty sure these are the passages they meant).
The first, from Moralia 18.90, combines the ideas of immutability and identity of essence and attributes:
But we are to know that there were some persons, who said that even in that region of blessedness God is beheld indeed in His Brightness, but far from beheld in His Nature. Which persons surely too little exactness of enquiry deceived. For not to that simple and unchangeable Essence is Brightness one thing, and Nature another; but Its very Nature is to It Brightness, and the very Brightness is Nature. For that to Its votaries the Wisdom of God should one day display Itself, He Himself pledges His word, saying, He that loveth Me, shall be loved of My Father, and I will love him, and will manifest Myself to him. [John 14, 21] As though He said in plain terms, ‘Ye who see Me in your nature, it remains that ye should see Me in Mine own nature.’ Hence He says again; Blessed are the pure in heart, for they shall see God. [Matt. 5, 8] Hence Paul says, For now we see through a glass darkly, but then face to face; now I know in part, then shall I know even as also I am known. [1 Cor. 13, 12]
The second (Moralia 16.54) also treats identity of essence and attributes:
What are called ‘the days’ of God, save His very Eternity itself? which is sometimes described by the announcement of ‘one day,’ as where it is written, For one day in Thy courts is better than a thousand. [Ps. 84, 10] But sometimes on account of its length it is represented by the expression of a number of days, whereof it is written, Thy years are throughout all generations. [Ps. 102, 24] We then are wrapped up within the divisions of time, through this that we are created beings. But God, Who is the Creator of all things, by His Eternity encompasses our times. And so he says, Times are not hidden from the Almighty; they that know Him, know not His days; seeing that He, indeed, sees all of ours to the comprehending thereof, but all that is His we are in no degree able to comprehend. But whereas the nature of God is simple, it is very much to be wondered at why he should say, They that know Him, know not His days. For it is not that He Himself is one thing and His ‘days’ another; since God is that thing which He hath.For He hath eternity, yet He is Himself Eternity. He hath Light, yet He is Himself His own Light. He hath brightness, yet He is Himself His own Brightness. And so in Him it is not one thing to be, and another thing to have. What does it mean then to say, They that know Him, know not His days,except that even they that know Him, do not know Him as yet? For even they who already hold Him by faith, as yet know Him not by appearance. And whereas He, Whom we truly believe, is Himself eternity to Himself, yet in what way there is that eternity of Him we know not. For in the thing that we hear touching the power of the Divine Nature, we are sometimes used to imagine such things as we know by experience. Thus every single thing that begins and ends, is bounded by the beginning and ending. And if it be by any little delay stayed from being ended, it is called long; on which same length whilst a man carries back the eyes of his mind in recollection, and stretches them out before in anticipation, as it were over a space of time he expands them in imagination. And when he hears the eternity of God mentioned in human sort, to his mind on the stretch he sets forth long spaces of life, in which same he may ever measure both what has gone away in the rear as a thing to be retained in the memory, and what remains before as a thing to be looked forward to in the intention.