Isaiah 6:8 - And I heard the voice of the Lord, saying: "Whom shall I send, and who will go for us?" Then I said: "Here am I; send me."
A trinitarian argues from the above the scripture that Isaiah heard the voice of Yahweh [in eternity past], and is referring to himself as more than one person.
Obviously, there is nothing here about these words being said in "eternity past". Such an idea has to be added to and read into what Isaiah said. If one would be consistent in following such reasoning, one would conclude that Isaiah himself had been hearing these words in "eternity past", and thus that Isaiah himself had existed in "eternity past" so as to be hearing these words in "eternity past".
We believe that Isaiah himself is playing a part in the prophetic role, depicting the church of Jesus who was yet to be. Each believer is depicted as hearing the voice of the Lord, asking, "Whom shall I send", and thus is depicted as responding: "Here am I."
The Masoretic text has "Adonai" (transliterated) where "the Lord" appears in most translations. The claim is made by some that this is one of the places copyists replaced Jehovah (Yahweh) with Adonai, and thus some translations have the Holy Name in the scripture. Nevertheless, the Great Isaiah Scroll does not have the holy name in Isaiah 6:8, but rather the Hebrew characters representing Adoni [transliterated, meaning "my Lord"] or Adonai [Literally, my Lords, used singularly, however, it means superlative or superior "Lord"].
At any rate, it is probable that Isaiah originally meant this to be "my Lord" [adoni], referring to the coming Lord of Isaiah [representing the believer]. From the New Testament, the coming "lord" is shown to be Jesus, the promised Messiah. In such a case, the words in question, who will go for us, appears to be those of Jesus directed toward his God, Jehovah. If so, the "us" refers to both Yahweh and Jesus. The one to "go" for them would be Isaiah (picturing the church individually). The fulfillment of the prophecy supports that ADNY (transliterated) in Isaiah 6:8 is not Jehovah, but Jesus.
This is in harmony with what Jesus said, for he recognized that no one could come to him except that his God and Father should draw such an one to Jesus.
John 6:44 - No one can come to me unless the Father who sent me draws him.
John 6:45 - Everyone who hears from the Father, and has learned, comes to me.
John 6:65 - No one can come to me, unless it is given to him by my Father.
The "us" would be both Jehovah and Jesus. The one to "go" for them would be represented by Isaiah, individually those who learn of Jehovah and come to Jesus.
However, the Great Isaiah Scroll does have the Hebrew word of God's name in Isaiah 6:11 -- not Adoni or Adonai. Thus it is possible that "the Lord" in Isaiah 6:8 is referring to Jehovah. Assuming that "the Lord" here is Jehovah, then this would only mean that Jehovah is simply speaking to Jesus, saying who will go for us?
Regardless, "us" would still be Yahweh and Jesus, and in no wise would mean that Jesus is Yahweh. If Tom says to his son, "Who will represent us in court?", is Tom saying he and his son are one sentient being?
Isaiah Saw His Glory