Isaiah 48:12-16
“Listen to Me, O Jacob, and Israel,
My called: I am
He, I am the First,
I am also the Last. Indeed
My hand has laid the foundation of the earth, and
My right hand has stretched out the heavens …
I, even
I, have spoken; yes,
I have called him,
I have brought him, and his way will prosper. Come near to
Me, hear this:
I have not spoken in secret from the beginning; from the time that it was,
I was there,
and now the Lord GOD and His Spirit have sent Me.”
Does the word "I" signify more than one person? How about the word "my"? How about the word "Me"?
Whoever is speaking is the
FIRST AND THE
LAST. The first and the last is obviously one person.
Jesus revealed to John who is the first and the last.
Rev 1:17
17And when I saw him, I fell at his feet as dead. And he laid his right hand upon me, saying unto me, Fear not; I am the first and the last: 18I am he that liveth, and was dead; and, behold, I am alive for evermore, Amen; and have the keys of hell and of death.
Jesus is the first and the last. He pre existed as YHWH in the OT. If the first and the last here is God the Father, Jesus is God the Father.
For some reason you left out verse 14. The one God has called in this context is Israel.
The last words of verse 16 concerning the one sent by the Lord God and his Spirit refers to Isaiah.
Note.
Isaiah 6:1-8
1In the year that king Uzziah died
I saw also the Lord sitting upon a throne, high and lifted up, and his train filled the temple. 2Above it stood the seraphims: each one had six wings; with twain he covered his face, and with twain he covered his feet, and with twain he did fly.
3And one cried unto another, and said, Holy, holy, holy, is the LORD of hosts: the whole earth is full of his glory.
4And the posts of the door moved at the voice of him that cried, and the house was filled with smoke.
5Then said I, Woe is me! for I am undone; because I am a man of unclean lips, and I dwell in the midst of a people of unclean lips: for mine eyes have seen the King, the LORD of hosts.
6Then flew one of the seraphims unto me, having a live coal in his hand, which he had taken with the tongs from off the altar: 7And he laid it upon my mouth, and said, Lo, this hath touched thy lips; and thine iniquity is taken away, and thy sin purged
8Also I heard the voice of the Lord, saying, Whom shall I send, and who will go for us? Then said I, Here am I; send me.
Isaiah sees the glory of the Adonai. In verse 8 it is clear Isaiah was the one who was sent by the Lord God and his Spirit.
John refers to this very thing in
John 12:37-41
37But though he had done so many miracles before them, yet they believed not on him: 38That the saying of
Esaias the prophet might be fulfilled, which he spake, Lord, who hath believed our report? and to whom hath the arm of the Lord been revealed? 39Therefore they could not believe, because that Esaias said again, 40He hath blinded their eyes, and hardened their heart; that they should not see with their eyes, nor understand with their heart, and be converted, and I should heal them.
41These things said Esaias, when he saw his glory, and spake of him.