I’ve been studying up and the doctrine of the Trinity in general and the deity of Jesus in particular. That study, obviously, led me to John 1:1. I think the NET Bible translation note sums up Wallace’s treatment quite nicely:
Or “and what God was the Word was.” Colwell’s Rule is often invoked to support the translation of θεός (qeos) as definite (“God”) rather than indefinite (“a god”) here. However, Colwell’s Rule merely permits, but does not demand, that a predicate nominative ahead of an equative verb be translated as definite rather than indefinite. Furthermore, Colwell’s Rule did not deal with a third possibility, that the anarthrous predicate noun may have more of a qualitative nuance when placed ahead of the verb. A definite meaning for the term is reflected in the traditional rendering “the word was God.” From a technical standpoint, though, it is preferable to see a qualitative aspect to anarthrous θεός in John 1:1c (ExSyn 266-69). Translations like the NEB, REB, and Moffatt are helpful in capturing the sense in John 1:1c, that the Word was fully deity in essence (just as much God as God the Father). However, in contemporary English “the Word was divine” (Moffatt) does not quite catch the meaning since “divine” as a descriptive term is not used in contemporary English exclusively of God. The translation “what God was the Word was” is perhaps the most nuanced rendering, conveying that everything God was in essence, the Word was too. This points to unity of essence between the Father and the Son without equating the persons. However, in surveying a number of native speakers of English, some of whom had formal theological training and some of whom did not, the editors concluded that the fine distinctions indicated by “what God was the Word was” would not be understood by many contemporary readers. Thus the translation “the Word was fully God” was chosen because it is more likely to convey the meaning to the average English reader that the Logos (which “became flesh and took up residence among us” in John 1:14 and is thereafter identified in the Fourth Gospel as Jesus) is one in essence with God the Father. The previous phrase, “the Word was with God,” shows that the Logos is distinct in person from God the Father.