In this comment on another blog Mo has claimed that classical reformed theologians were not interested in identifying which Person of the trinity is talking in the OT.
When it comes to appearances of the LORD and when it comes to the Angel of the LORD, that couldn't be further from the truth.
I could list many other quotes and many other theologians, but these will do for now:
Calvin in Institutes, I.xiii.10
The orthodox doctors of the Church have correctly and wisely expounded, that the Word of God was the supreme angel, who then began, as it were by anticipation, to perform the office of Mediator. For though he were not clothed with flesh, yet he descended as in an intermediate form, that he might have more familiar access to the faithful. …Hence it follows, that he is the God who was always worshipped by the Jews.
John Owen, Works, vol 18, p221 - discussing Genesis 18:
Neither is there any ground for the late exposition of this and the like places, namely, that a created angel representing the person of God doth speak and act in his name, and is called Jehovah; an invention to evade the appearances of the Son of God under the old testament, contrary to the sense of all antiquity, nor is any reason or instance produced to make it good.
Owen discussing Gen 19:24:
…in this place it is Moses that speaketh of the Lord, and he had no occasion to repeat ‘The LORD’ were it not to intimate the distinct persons unto whom that name, denoting the nature and self-existence of God, was proper; one whereof then appeared on the earth, the other manifesting his glorious presence in heaven… There is therefore in this place an appearance of God in human shape, and that of one distinct person in the Godhead, who now represented himself unto Abraham in the form and shape wherein he would dwell amongst men, when of his seed he would be ‘made flesh’. This was one signal means whereby Abraham saw his day and rejoiced; which Himself lays upon His pre-existence unto His incarnation, and not upon the promise of His coming, John 8:56, 58 (ibid, p222)
Owen discussing Jacob's wrestling:
From what hath been spoken, it is evident that he who appeared unto Jacob, with whom he earnestly wrestled, by tears and supplications was God; and because he was sent as the angel of God, it must be some distinct person in the Deity condescending unto that office; and appearing in the form of a man, he represented his future assumption of our human nature. And by all this did God instruct the church in the mystery of the person of the Messiah, and who it was that they were to look for in the blessing of the promised Seed. (ibid, p225)
Jonathan Edwards, A History of Redemption
When we read in sacred history what God did, from time to time, towards His Church and people, and how He revealed Himself to them, we are to understand it especially of the Second Person of the Trinity. When we read of God appearing after the fall, in some visible form, we are ordinarily, if not universally, to understand it of the Second Person of the Trinity... John 1:18. He is therefore called the image of the invisible God - Col 1:15 - intimating that though God the Father be invisible, yet Christ is His image or representation, by which He is seen.
John Owen especially uses the phrase 'distinct Person in the deity' very often when discussing the revelation of Christ as Mediator in the OT.
This insistence is not driven by any social trinitarianism but by solus Christus. Verses such as John 1:18; Colossians 1:15; Matthew 11:27 and, of course, John 14:6 were at the forefront of their thinking on this.
Whenever I see a departure from this classical reformed position on the Mediator's activity in the OT I fear a parallel departure from solus Christus in the strong form which the reformers held dear.
That's why I bang this drum.