Ok, I'll lay off the Spirit personage for now since it's not germane to the larger point I'm trying to make.
In the Isaiah passage someone is sending someone else. The someone being sent is the "LORD (Jehovah) the Redeemer", the some one doing the sending is "the Lord (Adonai) GOD (Jehovah)."
Is Jehovah sending Himself? Who is Adonai Jehovah sending and who is this Jehovah that is being sent?
It reads to me like He's sending Isaiah.