Since posting the following I have pointed to another detail that gives further reason to pause before assuming Lord = Jesus in Galatians.
but I saw none other of the apostles, but James the brother of the Lord.
Fear not. I will not here repeat the arguments that James was/was not the brother of Jesus. I have been through them often enough.
Here I will do nothing more than share a little datum that stubbed my toe as I was wandering through yet another tangent on another question. It returns us possibly to the very time period Paul is thought to have written his letter to the Galatians.
Many of us with an interest in the question know how often people cite that passage, without a second thought, as “James the brother of Jesus”. Who else could the Lord be?
So I was pulled up when I learned that such an unconscious bias is not limited to that one passage. In a scholarly study on another early Christian piece of writing, one that some scholars even consider to be possibly contemporary with the writings of Paul, the Didache, there is this footnote on the Didache’s use of the term “Lord God”:
Niederwimmer judges that “the Lord God” would have been intended in the original Jewish context but that here it refers to the “Lord Jesus” (Didache, 105). This demonstrates that even seasoned scholars can unknowingly transport into the Didache their bias in favor of identifying Jesus as Lord. They acquire this bias in studying Paul and in participating in Christian piety. It is difficult for them, accordingly, to imagine how the Didache can be true to Jesus while absolutely being centered upon the presence, the purposes, and the saving grace of the Father. Niederwimmer refers to the “original Jewish context” without even for a moment reflecting that Jesus himself and the movement he left behind were solidly rooted within a Jewish context.
Milavec, Aaron. 2015. “The Distress Signals of Didache Research: Quest for a Viable Future.” In The Didache: A Missing Piece of the Puzzle in Early Christianity, edited by Jonathan A. Draper and Clayton N. Jefford, 59–83. Atlanta: SBL Press. pp. 72f
Milavec reminds us that Jesus himself is said to have taught others to anticipate the coming of the Kingdom of God, that is, the God of the “Old Testament” where are found numerous prophecies that God himself, the one we might think of as the Father, was to descend to establish his rule on earth. Accordingly, we should keep in mind that Jesus’ earliest followers understood his references to Lord as references to the God he called Father.
It may sound a bit over the top to think that anyone would suggest James could be given a religious title associating him as something more than another “Friend of God” (as other biblical figures were known to be) but then again there is so much we don’t know about that early period. Among those who bequeathed to us the Gospel of Thomas James was said by Jesus to be the very person for whom heaven and earth came into being (GThom 12) — whatever that means. (Not to mention that in the second chapter of the same letter to Galatians Paul expresses his failure to be impressed by the status of James in the church and documents James representing a form of Christianity that he himself opposed.)
I’m not arguing that “brother of the Lord” definitely refers to God rather than Jesus. I am saying we have reasons not to be dogmatic and to always be willing to question our assumptions.
See also comment below: Milavec points out that it would have been blasphemous among those outside Paul’s followers to have called Jesus Lord.