Come near to Me, hear this: I have not spoken in secret from the beginning; from the time that it was, there I am. And now the Lord God has sent me and His Spirit.Isaiah 48:16 — Modern English Version (Thinline Edition.; Lake Mary, FL: Passio, 2014)
Perhaps what is present here is clear to you. In this portion of Isaiah, the prophet is speaking the words of God. He identifies Himself in the previous context as “I am the First, and I am the Last.” (Is 48:12)
Clearly, we can identify the One speaking in First Person here as God. We also know from other Scriptures in this portion of Isaiah this Person is the Maker, and He also ascribes Himself as Redeemer, Savior, and the Lord of Hosts. If we could identify the Person speaking by New Testament names, it’s Jesus!
If that is not clear, read the last line…
“And now the Lord God has sent me and His Spirit.”
One Person sent at least one other Person. I say that because it is clear in the text. Whether His Spirit is a person is not clear, but from the context it is hinted at.
What is apparent in reading through Isaiah, is there are two distinct Persons ascribed to God. The One speaking, Redeemer, was sent by the Lord God. And if the identity of the One sent is not clear, the next verse remedies that.
Thus says the Lord, your Redeemer, the Holy One of Israel: I am the Lord your God, who teaches you to profit, who leads you in the way that you should go.Isaiah 48:17 — Modern English Version (Thinline Edition.; Lake Mary, FL: Passio, 2014)
The first sentence tells you Who is speaking, and He gives not one, not two… not four… But three attributions to Who He is. Then He sums that up with the name of God YHVH.
Do not let anyone tell you the doctrine of the Trinity was made up by some New Testament “church fathers.” It is right there in the text. The old rabbis knew it, taught it and then suppressed it after Christ’s ascension.