The nominative case is the case that the subject is in. When the subject takes an equative verb like “is” (i.e., a verb that equates the subject with something else), then another noun also appears in the nominative caseąthe predicate nominative. In the sentence, “John is a man,” “John” is the subject and “man” is the predicate nominative. In English the subject and predicate nominative are distinguished by word order (the subject comes first). Not so in Greek. Since word order in Greek is quite flexible and is used for emphasis rather than for strict grammatical function, other means are used to distinguish subject from predicate nominative. For example, if one of the two nouns has the definite article, it is the subject.
As we have said, word order is employed especially for the sake of emphasis. Generally speaking, when a word is thrown to the front of the clause it is done so for emphasis. When a predicate nominative is thrown in front of the verb, by virtue of word order it takes on emphasis. A good illustration of this is John 1:1c. The English versions typically have, “and the Word was God.” But in Greek, the word order has been reversed. It reads,
kai; qeo;V h\n oJ lovgoV
and God was the Word.
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 qeovV 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.
To state this another way, look at how the different Greek constructions would be rendered:
kai; oJ lovgoV h\n oJ qeovV
“and the Word was the God” (i.e., the Father; Sabellianism)
kai; oJ lovgoV h\n qeovV
“and the Word was a god” (Arianism)
kai; qeo;V h\n oJ lovgoV
“and the Word was God” (Orthodoxy).
Jesus Christ is God and has all the attributes that the Father has. But he is not the first person of the Trinity. All this is concisely affirmed in kai; qeo;V h\n oJ lovgoV.