"If you do not believe that the nature/substance of the angels is the same as the Son because they were created but he was begotten, why do you believe the nature/substance of the Holy Spirit, who was neither created no begotten, is the same as the Son and the Father?"
Earnest, I believe that there is one God eternally existing and manifesting Himself to us in three persons--Father, Son and Holy Spirit.
John 14:9-20 "John 14:9 Jesus saith unto him, Have I been so long time with you, and yet hast thou not known me, Philip? he that hath seen me hath seen the Father; and how sayest thou then, Shew us the Father? Believest thou not that I am in the Father, and the Father in me? the words that I speak unto you I speak not of myself: but the Father that dwelleth in me, he doeth the works. Believe me that I am in the Father, and the Father in me: or else believe me for the very works' sake. Verily, verily, I say unto you, He that believeth on me, the works that I do shall he do also; and greater works than these shall he do; because I go unto my Father. And whatsoever ye shall ask in my name, that will I do, that the Father may be glorified in the Son. If ye shall ask any thing in my name, I will do it. If ye love me, keep my commandments. And I will pray the Father, and he shall give you another Comforter, that he may abide with you for ever; Even the Spirit of truth; whom the world cannot receive, because it seeth him not, neither knoweth him: but ye know him; for he dwelleth with you, and shall be in you. I will not leave you comfortless: I will come to you. Yet a little while, and the world seeth me no more; but ye see me: because I live, ye shall live also. At that day ye shall know that I am in my Father, and ye in me, and I in you."
This passage is proof that Jesus, the Father, and the Holy Spirit are ONE.
If you have seen Jesus, you have seen the Father.
The Father dwells in Jesus, Jesus dwells in the bosom of the Father. (John 1:18)
Jesus and the Father are one. Jesus, the Father, and the Holy Spirit are one.
This is quite obvious in this passage.
"He (the Father) will give you another Comforter (Holy Ghost)." Notice, the Comforter will dwell in them. Jesus says "he dwelleth with you", then he says "I shall be in you". He also says "I will come to you." Jesus will dwells in me, for the Holy Spirit dwells in me. For they are one. Jesus says "I am in my Father, and ye in me, and I in you." Jesus is one with the Holy Spirit, for if the Spirit dwells in you, Jesus dwells in you. And Jesus is one with the Father.
The Spirit is one with the Father.
Genesis 1:2 "And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters."
Ephesians 4:30 And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption.
Job 33:4 The Spirit of God hath made me, and the breath of the Almighty hath given me life.
So you see, the Holy Ghost, the Father, and the Son are one.
1 John 5:7 "For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one."