God: the one true God, Maker and Judge of everything there is, named so consistently in the New Testament that the word works almost like a personal name
Greek had this word long before the Bible, and it meant "a god," one of many. The writers of the New Testament took it over and used it, almost without exception, for one particular God: the God of Israel, who made the world and will judge it. They inherited that habit from the Greek translation of the Old Testament, where this word stands in for the ordinary Hebrew word for God (אֱלֹהִים) while God's personal covenant name (יהוה) is normally rendered by the word for Lord (κύριος).
That division of labor carries straight over. Across the New Testament, and in Paul above all, "God" points to the Father and "Lord" points to Jesus. So when Paul writes that for us there is one God, the Father, and one Lord, Jesus Christ, he is not demoting Jesus; he is spreading the words of Israel's great confession of faith across the two of them. Missing this habit is the commonest way to misread the word: it is not a general term for "the divine" but the name of someone with a history, promises, and a covenant people.
A small and carefully worded set of passages goes further and uses the word of Jesus himself. Only a couple of these are agreed by everyone; the rest are argued over, and the arguments usually turn on a punctuation mark or a manuscript reading rather than on what the word means. The senses below sort this out: the ordinary use for the one God, the sharpened use for the Father in particular, and the handful of places where the Son is called God.
Nuances
Whether the original text of John 1:18 read "the only God" (calling the Son God) or "the only Son".
- majorityThe reading "the only God" is original, on the strength of the earliest and best witnesses, and the shift to "Son" was a scribal simplification.; Murray J. Harris, Jesus as God: The New Testament Use of Theos in Reference to Jesus (Grand Rapids: Baker, 1992); Bruce M. Metzger, A Textual Commentary on the Greek New Testament, 2nd ed. (Stuttgart: United Bible Societies, 1994)
- minorityThe reading "the only Son" is original, and "God" is a later doctrinally motivated alteration.; Bart D. Ehrman, The Orthodox Corruption of Scripture (New York: Oxford University Press, 1993), 78-82
Whether the closing words of Romans 9:5 call Christ God over all, or form a separate blessing addressed to God the Father.
- contestedThe words apply to Christ, calling him God over all, which best fits the way the sentence is built.; Murray J. Harris, Jesus as God: The New Testament Use of Theos in Reference to Jesus (Grand Rapids: Baker, 1992); C. E. B. Cranfield, A Critical and Exegetical Commentary on the Epistle to the Romans, ICC (Edinburgh: T&T Clark, 1979)
- contestedThe words form an independent blessing of God the Father, since Paul nowhere else in his undisputed letters calls Christ God.; Bruce M. Metzger, A Textual Commentary on the Greek New Testament, 2nd ed. (Stuttgart: United Bible Societies, 1994)
Whether Hebrews 1:8, quoting Psalm 45, addresses the Son as God or instead says that God is the Son's throne.
- majorityThe words address the Son directly as God: your throne, O God, is forever.; Murray J. Harris, Jesus as God: The New Testament Use of Theos in Reference to Jesus (Grand Rapids: Baker, 1992)
- minorityThe words can instead be read as a statement, God is your throne, since the Greek of the psalm allows it.; Harold W. Attridge, The Epistle to the Hebrews, Hermeneia (Philadelphia: Fortress, 1989); B. F. Westcott, The Epistle to the Hebrews (London: Macmillan, 1889)
Disputed
How many New Testament passages use this word of Jesus, and how securely.
- majorityTwo are certain (John 1:1 and John 20:28), four more are very probable (Romans 9:5, Titus 2:13, Hebrews 1:8, 2 Peter 1:1), and John 1:18 is probable; the total is small but real.; Murray J. Harris, Jesus as God: The New Testament Use of Theos in Reference to Jesus (Grand Rapids: Baker, 1992); Raymond E. Brown, Does the New Testament Call Jesus God?, Theological Studies 26, no. 4 (1965): 545-573
- minorityThe total is smaller, because several of the probable passages turn on punctuation or on a disputed manuscript reading and are better taken of the Father.; Bruce M. Metzger, A Textual Commentary on the Greek New Testament, 2nd ed. (Stuttgart: United Bible Societies, 1994); Bart D. Ehrman, The Orthodox Corruption of Scripture (New York: Oxford University Press, 1993)