From another:
There’s always Dan Wallace’s blurb in the BBG,
We know that “the Word” is the subject because it has the definite article, and we translate it accordingly: “and the Word was God.” Two questions, both of theological import, should come to mind: (1) why was θεός thrown forward? and (2) why does it lack the article?
"In brief, its emphatic position stresses its essence or quality: “What God was, the Word was” is how one translation brings out this force. Its lack of a definite article keeps us from identifying the person of the Word (Jesus Christ) with the person of “God” (the Father). That is to say, the word order tells us that Jesus Christ has all the divine attributes that the Father has; lack of the article tells us that Jesus Christ is not the Father. John’s wording here is beautifully compact! It is, in fact, one of the most elegantly terse theological statements one could ever find. As Martin Luther said, the lack of an article is against Sabellianism; the word order is against Arianism
This verse is dealt with in more detail by Wallace, GGBB, pages 266–269."
Mounce, William D. Basics of Biblical Greek: Grammar. Ed. Verlyn D. Verbrugge. Third Edition. Grand Rapids, MI: Zondervan, 2009. Print.