This is yet another one of your proof texts that is a dual-usage proof text.Not really. Read chapter 48, especially where we have The Three distinct Persons, in verse 16, where the Speaker is Jesus Christ, the Father is Yahweh Adoni, and the Holy Spirit. Read the preceding verses, and you will see that Jesus says that He Created!
12 Hearken unto me, O Jacob, and Israel my called: I am he; I am the first, I also am the last. 13 Yea, my hand hath laid the foundation of the earth, and my right hand hath spread out the heavens: when I call unto them, they stand up together
Jesus also says that He is "The First and The Last", which means ETERNAL, as YHWH.
I say Isaiah 48 is proof that God is one individual and you claim "No, that's Christ speaking there." with no provable evidence.
How can you prove that Christ is speaking there, but Christ is not the Father - especially when Isaiah himself states that He IS in Isaiah 9:6?