What is the substance/nature of God based on Trinitarians?

The Trinity; or the God head; as we Baptist often refer has no material substance since He (as we often refer to God) is a Spirit. But does have substance in the Spiritual Realm.

According to Merriam Webster:

SUB'STANCE, n. [L. substantia, substo; sub and sto, to stand.]

1. In a general sense, being; something existing by itself; that which really is or exists; equally applicable to matter or spirit. Thus the soul of man is called an immaterial substance, a cogitative substance, a substance endued with thought. We say, a stone is a hard substance, tallow is a soft substance.

It is this definition of substance that we must assign to the Trinity.

Notice that in Latin the it means to stand, and if we apply that standard to the Spiritual Realm to which the Trinity belongs it has meaning other than in the material realm.

Exodus 3:14 NKJV And God said to Moses, "I AM WHO I AM." And He said, "Thus you shall say to the children of Israel, 'I AM has sent me to you.' "

This is what God meant when:

Genesis 1:26 NKJV Then God said, "Let Us make man in Our image, according to Our likeness; let them have dominion over the fish of the sea, over the birds of the air, and over the cattle, over all the earth and over every creeping thing that creeps on the earth."

Since God has no Material substance what He must be referring to is his Spiritual substance or what could be called his nature referring to his Spiritual characteristics. When Moses asked him who should he say sent him; the LORD replied:

Exodus 3:14 NKJV And God said to Moses, "I AM WHO I AM." And He said, "Thus you shall say to the children of Israel, 'I AM has sent me to you.' "

God knew that if He were to present himself in some form, which they would understand, it would of necessity have some resemblance to something their minds could envision, and would therefore require some material reference.

Even to this day we have no real concept of the Trinity since we refer to it as **the Father, the son, and the Holy Ghost. None of these is truly descriptive of God in any of his three forms. The minds of man cannot adequately imagine something which has no shape or form, but exists as pure intelligence and power. The same is true of man's soul which is truly God's image just as Webster described it:

Thus the soul of man is called an immaterial substance, a cogitative substance, a substance endued with thought.

In fact the human mind is incapable of envisioning nothing, it has to have some reference to compare, and there is no counterpart to nothing. as an exercise try to conjure up in your mind neither darkness or light, but pure intelligence, and you will always seek something to compare it to, and yet that is the realm in which God exists.

I among others have attempted to envision God in that way, but are unable to, since it is totally contrary to the World we know. let alone trying to imagine it existing in three parts.

The substance/nature of God is truly inexplicable and is why God said:

Isaiah 55:8 and 9 NKJV "For My thoughts are not your thoughts, Nor are your ways My ways," says the LORD. 9 "For as the heavens are higher than the earth, So are My ways higher than your ways, And My thoughts than your thoughts.

Hope this helps

The Greek word θεός⁽¹⁾ may refer to the essence (οὐσία) of Yahveh, or to the person (ὑπόστασις) of Yahveh (i.e., to Yahveh Himself). "Yahveh" is the name of the person; θεός (or "god," אלהים, deus) is what Yavheh is (i.e., Aquinas' quidditas or Aristotle's τὸ τί ἦν εἶναι and/or secondary οὐσία).

In his Exact Exposition of the Orthodox Faith, §3.4, John of Damascus wrote,

"We have frequently stated that essence (οὐσία) is one thing and hypostasis (ὑπόστασις) another, and that essence (οὐσία) signifies the common and general species (εἶδος) of hypostases of the same species (ὁμοειδῶν), such as "God" (θεός), "man" (ἄνθρωπος), but hypostasis (ὑπόστασις) signifies the individual, that is to say, "Father," "Son," "Holy Spirit," "Peter," "Paul." Well then, one must know that "divinity" (θεότητος) and "humanity" (ἀνθρωπότητος) are names of essences (οὐσιῶν) (or natures) (φύσεών), but "God" (θεὸς) and "man" (ἄνθρωπος) are applied in reference to natures (φύσεως), whenever we say, "God is an incomprehensible essence," and "God is one." But, it is also understood of in reference to hypostases (ὑποστάσεων), when the name of the more universal is applied to that which is more particular, as when the scripture says (Psa. 45:7), "Therefore, O' God, your God has anointed you..." (for behold, it indicates the Father and the Son), and as when it states, (Job 1:1), "There was a certain man in the land of Uz" (for, it only indicated Job)."

Ὅτι μὲν οὖν ἕτερόν ἐστιν οὐσία καὶ ἕτερον ὑπόστασις, πλειστάκις εἰρήκαμεν, καὶ ὅτι ἡ μὲν οὐσία τὸ κοινὸν καὶ περιεκτικὸν εἶδος τῶν ὁμοειδῶν ὑποστάσεων σημαίνει οἷον θεός, ἄνθρωπος, ἡ δὲ ὑπόστασις ἄτομον δηλοῖ ἤτοι πατέρα, υἱόν, πνεῦμα ἅγιον, Πέτρον, Παῦλον. Ἰστέον τοίνυν, ὅτι τὸ μὲν τῆς θεότητος καὶ τῆς ἀνθρωπότητος ὄνομα τῶν οὐσιῶν ἤτοι φύσεών ἐστι παραστατικόν, τὸ δὲ θεὸς καὶ ἄνθρωπος καὶ ἐπὶ τῆς φύσεως τάττεται, ὁπόταν λέγωμεν· Θεός ἐστιν ἀκατάληπτος οὐσία, καὶ ὅτι εἷς ἐστι θεός· λαμβάνεται δὲ καὶ ἐπὶ τῶν ὑποστάσεων ὡς τοῦ μερικωτέρου δεχομένου τὸ τοῦ καθολικωτέρου ὄνομα, ὡς ὅταν φησὶν ἡ γραφή· «Διὰ τοῦτο ἔχρισέ σε ὁ θεὸς ὁ θεός σου» (ἰδοὺ γὰρ τὸν πατέρα καὶ τὸν υἱὸν ἐδήλωσε), καὶ ὡς ὅταν λέγῃ· «Ἄνθρωπός τις ἦν ἐν χώρᾳ τῇ Αὐσίτιδι» (τὸν γὰρ Ἰὼβ μόνον ἐδήλωσεν).

In his Commentary on the Apostle's Creed, §4, Rufinus wrote,

"God," so far as the human mind can form an idea, is the name of that nature or substance which is above all things.

Deus, secundum quod opinari potest humana mens, naturae ipsius, vel substantiae, quae est super omnia, appellatio est.

^{(You have to understand that the Latins often wrote as though substantia was synonymous with οὐσία.)}

All this being said, your question would have been better worded had it asked, "What is the substance/nature of Yahveh (insert your preferred name of God here) according to Trinitarianism?" Of course, if you use "God" in the sense of the more particular, rather than the more general, it is an acceptable question.

Footnotes

⁽¹⁾ and thus the English word "god," Hebrew word אלהים, and Latin word deus.