Gieschen's conclusion gives his reason for writing:
If we are convinced that the Son is central to the identity of YHWH as he speaks and acts throughout the Old Testament, we can and should show forth the pre-incarnate Son when preaching from the Old Testament. To do this we do not need to have a messianic or typological prophecy in the text, nor do we need to set up elaborate comparisons between God in the Old Testament and then fast-forward to Christ in the New Testament. We can also let those to whom we preach see Christ by showing them the real presence of the Son in Old Testament events and speech.
Interesting within the article is Gieschen's recognition of Augustine as deviating from the christocentric OT interpretation prevalent in the early church:
It was Augustine who solidified the position against seeing the Son, or any other person of the Trinity, as visibly present in the theophanies of the Old Testament. He argued that the manifestations of God in Old Testament events were mediated by angels:
The Father, the Son, and the Holy Spirit, since it is in no way changeable, can in no way in its proper self be visible. It is manifest, accordingly, that all those appearances to the fathers, when God was presented to them according to his own dispensation, suitable to the times, were wrought through the creature. And if we cannot discern in what manner he wrought them by ministry of angels, yet we say that they were wrought by angels. (On the Trinity 3.21-22)
Augustine, writing between A.D. 400-420, is obviously reacting against those who were using the theophanies to prove the created nature of the Son or the difference of his essence from the Father. Unlike the Formula of Sirmium in the mid-fourth century, which included anathemas against anyone who denied that it was the Son who appeared to Abraham and Jacob, Augustine called for a much more moderate understanding:
We should not be dogmatic in deciding which person of the three appeared in any bodily form or likeness to this or that patriarch or prophet, unless the whole context of the narrative provides us with probable indications. In any case, that nature or substance, or essence, or whatever else you may call that which God is, whatever it may be, cannot physically be seen; but on the other hand we must believe that by creature control the Father, as well as the Son and the Holy Spirit, could offer the senses of mortal men a token representation of himself in bodily guise or likeness. (On the Trinity 3.25)