In a rather pathetic attempt to support the Trinity from the Old Testament, Nabeel Qureshi wrote the following:
[A]n example of a passage in the Old Testament that features the deity of all three persons of the Trinity can be found in Isaiah 48:12-16. The clarity of the statement can be lost because of the many statements emphasizing the sovereignty of the speaker, but if we remove the intervening statements, the passage reads: “’I am he; I am the first and the last. Indeed, my own hand established the earth . . .’ and now the Lord God and his Spirit have sent me.” Here, the Alpha and the Omega says he was sent by the Lord God along with his Spirit. The next verse calls the speaker “Yahweh,” “Redeemer,” and “the Holy One of Israel.” In this passage, Yahweh is sent by Yahweh and the Spirit of Yahweh, and this makes little sense unless rea through the lens of the Trinity. (Nabeel Qureshi, No God but One: A Former Muslim Investigates the Evidence for Islam and Christianity [Grand Rapids, Mich.: Zondervan, 2016], 59)
Firstly, one cannot help but notice the inanity of Qureshi’s proposal: there is one Yahweh who is sent by a second Yahweh and another person who is the Spirit of Yahweh. That results in three Yahwehs, not three persons within a single Yahweh(!)
Jaco van Zyl, a “Biblical Unitarian,” wrote the following, which captures why appealing to Isa 45:5 and other like-texts in “Deutero-Isaiah” poses a problem for Trinitarian claims:
Trinitarians like James White argue that Yahweh (Adonai) speaks to someone else who is also Adonai. However they want to look at it, this is troublesome even to Trinitarian theology: If Yahweh is 3-in-1 God, speaking to another Adonai adds between 1 and 3 to the existing 3, leaving us with between 4 and 6 Persons in one God. If, however, you add the second Adonai to the first, then Yahweh is 2 and not 3 Persons, isn’t He (or should I say they)? (Jaco van Zyl, "Psalm 110:1 and the Status of the Second Lord--Trinitarian Arguments Challenged," in An E-Journal from The Radical Reformation: A Testimony to Biblical Unitarianism, pp. 51-60, here, p. 60).
Secondly, Qureshi is guilty of quote-mining Isaiah text; in reality, it is Israel, not Yahweh (or a person of the “being” of Yahweh or however one wants to put it) who is sent by Yahweh and His Spirit. Here is the text of the pericope from the NRSV:
Listen to me, O Jacob, and Israel, whom I called: I am He; I am the first, and I am the last. My hand laid the foundation of the earth, and my right hand spread out the heavens; when I summon them, they stand at attention. Assemble, all of you, and hear! Who among them has declared these things? The Lord loves him; he shall perform his purpose on Babylon, and his arm shall be against the Chaldeans. I, even I, have spoken and called him, I have brought him, and he will prosper in his way. Draw near to me, and hear this" From the beginning I have not spoken in secret from the time it came to be I have been there. And now the Lord God has sent me and his spirit.
This is further strengthened when one reads Isa 48:17-49:4:
Thus says the LORD, your Redeemer, the Holy One of Israel: I am the LORD your God, who teaches you for your own good, who leads you in the way you should go. O that you had paid attention to my commandments! Then your prosperity would have been like a river, and your success like the waves of the sea; your offspring would have been like the sand, and your descendants like its grains; their name would never be cut off or destroyed from before me. Go out from Babylon, flee from Chaldea, declare this with a shout of joy, proclaim it, send it forth to the end of the earth; say, "The LORD has redeemed his servant Jacob!" They did not thirst when he led them through the deserts; he made water flow for them from the rock; he split open the rock and the water gushed out. "There is no peace," says the LORD, "for the wicked." Listen to me, O coastlands, pay attention, you peoples from far away! The LORD called me before I was born, while I was in my mother's womb he named me. He made my mouth like a sharp sword, in the shadow of his hand he hid me; he made me a polished arrow, in his quiver he hid me away. And he said to me, "You are my servant, Israel, in whom I will be glorified." But I said, "I have labored in vain, I have spent my strength for nothing and vanity; yet surely my cause is with the LORD, and my reward with my God."
In Isaiah, Israel, or "Jacob," is Yahweh's servant and routinely depicted as a single man. It is quite clear that "ME" at Isaiah 48:16 is Yahweh's servant Israel.