In its comment on John 8:24, The Moody Bible Commentary reads:
The Moody Bible Commentary - John 8:24
Twice in this verse, the Lord stated that those who remain in unbelief will die in their sins. For the unbeliever, nothing changes when he dies; he remains a sinner for eternity. The words I am He (ego eimi; "I Am") contain terms peculiar to the Fourth Gospel and significant to Jesus' explicit self-declaration of deity (see comments on vv. 28, 58). Some have objected that the phrase ego eimi is not referring to deity but has an implicit completion, such as, "if you do not believe I am who I claim to be" or "if you do not believe that I am not of this world but from above" you are still in your sins. However, these translations are unlikely since the sentence does not include a grammatical object. The alternative possibility, that Jesus was declaring his own deity, is far more likely.
The phrase ego eimi is probably not a reference to Ex 3:14 (I AM WHO I AM) because the LXX translates the phrase "I Am has sent me" with the Greek words ho on ("the Existing One has sent me") rather than using ego eimi. More likely it is taken from the LXX's consistent usage of ego eimi as the translation of ani hu ("I am He"), a phrase used for God's self-disclosure in Isaiah (cf. Is 41:4; 43:10, 13, 25; 46:4; 48:12). For example in Is 43:10, the Lord says, "So that you may know and believe Me, and understand that I am He (ani hu)." Jesus applied the words of God's self-identification in the OT to Himself.
Above, the Moody Bible Commentary begins by stating that it is unlikely that Jesus saying "I am He" means something like "I am who I claim to be", or "I am not of this world but from above", because "the sentence does not include a grammatical object". However, the Greek term ego eimi is only necessarily a term of self-identification, and even the formerly-blind man in John 9 uses it without an explicit grammatical object (John 9:9). Context determines what the identification means, because grammatically, the term ego eimi is ambiguous without referencing the context.
In context, Jesus has said, "I am the light of the world" (John 8:12), and as noted in the commentary, in the verse just before the passage in question, He says, "You are from beneath. I am from above. You are of this world. I am not of this world" (John 8:23). Either of these statements would be better candidates for what Jesus is referring to in John 8:24, and would be a self-identification of His divine ordination as God's Messiah. The theme of Jesus being "sent" from Heaven, or from God, is a consistent pattern in the Gospel of John (John 3:17, 5:23-24, 5:30, 6:29, 6:38-39, 7:28-29, 8:29, etc.), and these statements fit into that pattern.
Then, the Moody Bible Commentary proceeds to argue that Jesus's statement is probably not a reference to the "I Am" statement of God in Exodus 3:14, noting that the Septuagint does not read ego eimi in the second part of Exodus 3:14 (although the first part of the passage does contain the phrase ego eimi).
Instead, the commentary argues that the "I am" statements in the latter part of the book of Isaiah are better candidates for what Jesus was referencing, and cites from the following passages to demonstrate their point:
Isaiah 41:4 (WEB)
4 Who has worked and done it, calling the generations from the beginning? I, Yahweh, the first, and with the last, I am he."
Isaiah 43:10-11 (WEB)
10 "You are my witnesses," says Yahweh, "With my servant whom I have chosen; that you may know and believe me, and understand that I am he. Before me there was no God formed, neither will there be after me.
11 I myself am Yahweh; and besides me there is no savior.
Isaiah 43:12-13 (WEB)
12 I have declared, I have saved, and I have shown; and there was no strange god among you. Therefore you are my witnesses," says Yahweh, "and I am God.
13 Yes, since the day was I am he; and there is no one who can deliver out of my hand. I will work, and who can hinder it?"
Isaiah 43:25 (WEB)
25 I, even I, am he who blots out your transgressions for my own sake; and I will not remember your sins.
Isaiah 46:3-4 (WEB)
3 "Listen to me, house of Jacob, and all the remnant of the house of Israel, that have been borne from their birth, that have been carried from the womb;
4 and even to old age I am he, and even to gray hairs will I carry you. I have made, and I will bear; yes, I will carry, and will deliver.
Isaiah 48:12-13 (WEB)
12 "Listen to me, O Jacob, and Israel my called: I am he; I am the first, I also am the last.
13 Yes, my hand has laid the foundation of the earth, and my right hand has spread out the heavens: when I call to them, they stand up together.
Firstly, notice that in the context of each verse above, God makes a statement as to who He is (bolded), and somewhere in the context says the phrase "I am", which refers to the identity that He states in the context. If this same practice were applied to the passage in question from John chapter 8, then Jesus would be saying that He is "from above" (John 8:23), as that is the immediate context of His "I am" statement in John 8:24.
But, notice the general tenor of the Trinitarian argument that is being made. Instead of interpreting what Jesus says in light of His ego eimi statement in John 4:25-26, where He uses it to identify Himself as the Christ, or in light of His identity statement in John 8:23 that He is "from above", the commentary goes back to the book of Isaiah - not only to argue for a similar pattern, but to assert that Jesus is both using a similar pattern, and that His doing so means that He is the same one speaking in the Isaiah passages. This is a massive over-reading of the text. Even if one were to demonstrate that John's "I am" statements are intended to parallel the ones in Isaiah, it still would take much more to demonstrate that such a parallel would mean that Jesus just is God.
In summary, the Moody Bible Commentary's understanding of John 8:24 cannot be justified in the context of the Gospel of John, which is not confused as to who the one God is (John 17:3). Jesus's statement in John 8:24 is one of self-identification as the one sent from Heaven, the Messiah, and believing in Him as that one is what saves one from their sins (John 20:30-31).