The Father and the Son are equal in substance.
The SUBSTANCE of God was a Greek philosophical endeavor, for good reason not a subject of debate for the ancient Jew, and for good reason. NO MAN knows one iota of what this is, much less being able to functionally discriminate something like a combined OUSIA or HOMOOUSIA. Take His heart, for instance. What can you say about it? For the Jew, the heart and mind are the same thing. So then what can we know or say about God's mind? Nada, nilch, zero, less than nothing. What is less than nothing? The speculations of men, because they represent the optimistic going of man into the land of monsters, false premises and tyranny. Tyranny of what? Your own mind, sir.
God's existence is echad, as God, numerically a single unit. But more importantly, "YWHW" is His identity as name. The Shema prohibits any other consideration THAN this identity as being alone, unique, by itself as a single thing. Is God a THING? Well, in the exalted sense, yes. A living entity of life, ruach, consciousness, knowing and commanding.
They have different roles, however, and such would make one believe one was superior to the other, but this is not the case. The Father is the eternal originator of the Trinity.
"My Father is greater than all." What does this portray? His ONTOLOGY? No. His AUTHORITY? Yes. His EXISTENCE in authority? Yes. The implication is to substance, or kind of, categorization of, species of. But directly said, not exactly. As a whole existence, the Father is above the Son in all ways.
1 Cor 15
25 For he must reign, till he hath put all enemies under his feet.
26 The last enemy that shall be destroyed is death.
27 For he hath put all things under his feet. But when he saith all things are put under him, it is manifest that he is excepted, which did put all things under him.
28 And when all things shall be subdued unto him, then shall the Son also himself be subject unto him that put all things under him, that God may be all in all.
So then is it Jesus' HUMANITY only subject to God? No, the above verse 28 refutes this.
And the Father did not exist before the Son. The Father eternally begets the Son.
A quasi-moto rationale DESIGNED to make trinity cohesive, SINCE it was forced upon the original meanings. "Eternal begotteness," is hokey, blokey and smokey.
Makes no sense. Jesus was pre-existent in the intent or determination of God only, the abstract sense of Sovereign Will, otherwise no prophet could foretell of Messiah.
John 17:5 - And now, Father, glorify me in your presence with the glory I had with you before the world began.
A reference to God's Determined Messiah. Jesus' glory was predetermined before the world was. He had no original input into his own creation as a babe who loved God from his mother's breast, Psalm 22.
John 8:58 - Jesus said to them, “Most assuredly, I say to you, before Abraham was, I AM.”
"I am Theology" is as hokey as anything in the ethers. Neither from the Hebrew does it make sense, Exodus 3 parallel: eyeh ashr eyeh, in the INDEFINITE tense or I WILL BE what/whom I WILL BE, or "I am being what I am being"...or from the Koine: "I am [he]," said at least four other times in John without a compliment, does this mean "I am." Also, "tell them the I AM sent you," second clause in Exodus 3, is HO OWN, "the Being." NOT "I am." This is Septuagint translation of Exodus 3.
I AM indicates the Name of God.
JEHOVAH is more accurate, and has no to be verb meant or statement of existence at all, except in the form ieue, compared to the to be verb, aeie "I will be" (unto the Hebrews) The Hebrew is not translatable except as a unique name of God.
Jesus existed before the world, with the Father. The Father is the originator of the Trinity. However, the Son has always eternally been begotten by the Father and the Spirit eternally proceeding from the Father. So the Father did not exist before the Son or the Spirit.
Worlds existed before our world, else the angels would have no world of existence. You smudge Judaic pre-existence with eternal pre-existence.
Jesus does not have physical limits. Despite living on the earth in a fleshly body, His divine nature was still omnipresent, omnipotent and bearing all of those qualities of God. Nevertheless, Jesus now has a glorified body, and it is not limited by space and time.
The Holy Spirit is this in Jesus only, in the sense he was MADE a life-giving spirit only. And the Holy Spirit was ever emanated or SENT of the Father.
Matthew 19:17 is actually used to support the notion that Jesus was God, because Jesus says elsewhere, in John 10:11, that He is the 'good shepherd'.
No proof at all that Jesus is God.
Hebrews 1 and 1 Corinthians 15 merely demonstrate that the Father and Son have different roles.
Your "merely" is Jesus' absolutely. "My Father is greater than all."