Part 3 of this ongoing series will focus primarily on Dr. Douglas F. Kelly's contributions concerning "The angel of the Lord" (Jehovah) and "Theophanies", published in his Systematic Theology - Volume One (2008 - Google Books).
Dr. Kelly begins his section on the "angel of the Lord" at page 465:
The angel of the Lord
Angels in both Old and New Testaments are usually 'messengers of God', often, 'ministering to those who are heirs of salvation' (Heb. 1:14). They are created spirits who can at times appear in human form. But they can also be identified with God Himself. Such is the case with the angel who speaks to Hagar, promising, 'I will multiply thy seed exceedingly' (Gen. 16:7). The, after the angel leaves, Hagar 'called the name of the LORD that spake unto her, Thou God seest me...' (v. 13). At the sacrifice of Isaac (which was divinely prevented), the angel of the LORD said to obedient Abraham: 'I know that thou fearest God, seeing thou hast not withheld thy son, thine only son from me' (Gen. 22:12). Not to withhold Isaac from the angel was not to withhold him from God Himself. Thus, theangel is identified with the Lord. Jacob in his strange night of wrestling with 'a man' Genesis 32:30 (who is termed 'angel' in Hosea 12:4) says: 'I have seen God face to face, and my life is preserved.' The 'angel of the Lord' speaks to Jacob in Genesis 33:10-31, and makes it clear that He is the same as 'the God of Bethel.' Moses met the angel of the Lord in the burning bush, which was the same as meeting the Lord (Exod. 3:2-6). After the people of God had entered the Promised Land, the angel of the Lord says: '... I made you to go up out of Egypt, and have brought you into the land which I sware unto your fathers; and I said, I will never break my covenant with you' (Judg. 2:1). Malachi 3:1, identifies the messenger (or angel) of the covenant with God Himself: 'Behold, I will send my messenger, and he shall prepare the way before me: and the Lord, whom ye seek, shall suddenly come to his temple, even the messenger of the covenant, whom ye delight in: behold, he shall come, saith the LORD of hosts.'
As Herman Bavinck writes:
... the subject which speaks through the angel of Jehovah far surpasses a created angel. The church-fathers before Augustine were unanimous in explaining this Angel of Jehovah as a theophany of the Logos...So much is clear: that in the Mal'akh Yhwh who is pre-eminently worthy of that name, God (esp. his Word) is present in a very special sense. This is very evident from the fact that though distinct from Jehovah this Angel of Jehovah bears the same name, has the same power, effects the same deliverance, dispenses the same blessings, and is the object of the same adoration. 
Thus, the mysterious appearance of the angel of the Lord indicates a certain diversity within the one Being of God, for He is at the same time both distinct from God and also one with God. Such passages indicate that God's Being is not an impoverished monad. Instead, His Being has a rich inner diversity.
53. Herman Bavinck, The Doctrine of God, translated by William Hendriksen (Edinburgh: The Banner of Truth Trust, 1979 reprint), 257.
The OT passages quoted by Dr. Kelly, when reflected upon with the assessment from Dr. Bavinck in mind, seems to modify an absolute understanding that all the references to the 'Angel of Jehovah' have a created angel in mind (contra Augustine).
Dr. Kelly immediately follows the above with his take on "Theophanies":
Some of the appearances of holy angels are traditionally called 'theophanies' (i.e. manifestations of God). 'In these theophanies we note that on occasions the A. V. or the LXX speak of an angel, and sometimes the angel. This is no discrepancy, of course, but merely two ways of translating the Hebrew construct state.'  Knight goes on to list fifteen theophanies. We have already discussed several of them (i.e. Gen. 16:7-14; 21:17-19; 22:11-18; 31:11-13; 32:4-12; Exod. 3:2-6; Judg. 2:1-5).
54. George F. Knight, A Biblical Approach to the Doctrine of the Trinity, 25.
Dr. Kelly then examines 9 more passages: Gen. 18:1-22; 19:1; 48:15-16; Exod. 14:19-22; Josh. 5:13-16; Judg. 6:11-24; 13:2-23; Zech. 1:12; and 3:6-10. (Page 466.)
He concludes this section with the following assessment:
Before the rise of biblical higher criticism, the Christian theological tradition, both East and West, Catholic and Protestant, generally understood the Old Testament theophanies to be pre-incarnate appearances of the Second Person of the Trinity, Christ Himself. The nineteenth-century Swiss Reformed scholar, Louis Gaussen, helpfully summarized much of the traditional interpretation on this point, as we see in Appendix II to this chapter. (Page 467.)
From the above mentioned appendix, we read:
Chapter Seven Appendix Two - The Traditional Christian Interpretation of Old Testament Theophanies as Pre-Incarnate Appearances of Christ (as summarized by Louis Gaussen) [From Louis Gaussen, Sermons par Gaussen, 1847.]
In the main part of Chapter 7 we considered some Old Testament passages that speak of the mysterious angel of the Lord, and undertood them to be intimations of the pre-incarnate Son of God. But more remains to be said about this foreshadowing of the Holy Trinity. Dr. Louis Gaussen has carefully explicated the appearances of the angel of the Lord in a relatively brief compass. (Page 479.)
Dr. Kelly then translates the germane portion from Gaussen's, "Gédéon devant l'Ange de l'Eternal" [from the French in, Sermons par Gaussen, 1847.]
In the selection provided by Dr. Kelly, Gaussen lists, "several very simple principles, by which we may grasp in a very precise and certain manner the right opinion on this important subject" (pp. 479-483). Of the five that he provides, the following is the first:
The first of these principles is nothing else than one fact; here it is: every time in the Holy Bible that we are faced with appearances of this mysterious Angel, whom the Holy Spirit calls 'the Angel of the Face' (Isa. 63:9); 'the Angel of the Covenant' (Mal. 3:1), or 'the Angel of the LORD God' or 'Angel of Jehovah', one understands Him to be attributing constantly all the most incommunicable names of the omnipotent God; and not only the names, but also His attributes and works; and not only His attributes, names, and works, but also the worship which everywhere God claims for Himself alone. (Pages 479, 480.)
The second principle, "is the principle of divine unity." The third, "will be only one assertion, which flows directly from the first two, and which is nearly the same as they are. Here it is: The Being who, in the Bible, attributes to Himself the names, the works. the characteristics, and even the worship of almightly God, cannot be a creature." (Page 481.)
The fourth, "which is no less questionable: THE ANGEL OF HIS FACE, who appears so often to the elect of God in the Old Testament, could not be God the Father." (Page 481.)
And the fifth:
It was the Angel of the LORD, O Christians, it was the same Saviour, the same Master, the Comforter, whom we are commissioned to proclaim in the flesh; and also it was therefore already He who was appearing before His incarnation, in preparation for His mission of incomprehensible abasement in which He would come down at a later time in order to save us. (Page 481.)
Gaussen provides additional commentary and Scriptural support for all five principals. At end of his translation, Dr. Kelley adds the following summary:
Most Old Testament scholars for the last century (even conservative ones) have been considerably more restrained in definitely identifying all appearances of the angel of the Lord as the pre-incarnate Christ. Even if Gaussen is at times overconfident in focusing the scope of all passages he quotes exclusively to the Second Person of the Trinity, still, I cannot see that he is essentially wrong either exegetically or theologically, in assuming that in most cases of theophanic appearances of the angel of the Lord, the pre-incarnate Christ is most likely referred to. Many Church Fathers, medieval scholastics, and sixteenth-century Reformers held to much the same understanding of the angel of the Lord, and I can find no compelling reason to part company with them on this point. (Page 483.)
The conviction held by the ante-Nicene Church Fathers, Gaussen, Gill, Hengstenberg, Liddon, et al., that, "in most cases of theophanic appearances of the angel of the Lord, the pre-incarnate Christ is most likely referred to", is also my view; and like Dr. Kelly, "I can find no compelling reason to part company with them on this point."
Grace and peace,