Brian LePort has posted on one of the different manuscript readings in Acts 20:28. For those who may be new to the topic, there are two important variants in that verse in the Greek manuscripts we have. On the one hand, manuscripts vary on reading “church of God” or “church of the Lord.” On the other hand, in some manuscripts, the phrase “his own blood” is worded in such a way that it can mean “the blood of (the one who is) his own.” (For some of the variations in the Syriac, see here).
In deciding what the original reading is likely to have been in these instances, perhaps the most important thing to consider is that there has been nothing, absolutely nothing, in Luke or Acts that has depicted Jesus as God. And so it seems safe to say that the reading “the church of God, which he bought with his own blood” is not original.
In the Christology of Luke-Acts, Jesus is a human being who is empowered with the Holy Spirit during his life, and raised from the dead and exalted to heaven after the end of his life. There is no point at which Jesus is depicted as being pre-existent or the incarnation of a pre-existent entity. (In fact, the only person who makes such a claim for himself in Luke-Acts is Simon Magus).
And so this instance illustrates how a careful study of a work’s Christology can allow the textual critic to draw conclusions about the likely direction of alteration. In this case, Luke’s wording has been changed over the course of transmission to agree with developing orthodoxy, rather than vice versa.