As many Trinitarians admit, while a distinction between the "persons" of the Trinity is tolerated (with great ambiguity; even the definition of "person" is debated), a distinction between "God" (or any other names/titles of deity) and any of the persons tends not to be tolerated. Notwithstanding, this is what we see time and time again throughout the New Testament, such as John 17:3, where the person of the Father is said to be in the category of "only true God," and the words of Paul in 1 Cor 8:4-6 (discussed here) and 1 Tim 2:5 that draws a distinction between "God" (not just the person of the Father) and Jesus, attempts to rehabilitate the Trinity through the concept of "divine identity" (á la Richard Bauckham, refuted by Dale Tuggy here) notwithstanding.
On John 17:3 and its Christological implications, as I wrote elsewhere:
Gilpin has used a text that refutes, not supports, his Christology Why? Firstly, one should note that in Trinitarian theology, there is an allowance (albeit, ambiguously) for a distinction between the “persons” of the Godhead (the Father is not the Son; the Son is not the Spirit; the Spirit is not the Father), as modalism would arise if no distinction was permitted between them; however, there is no allowance for a distinction between “God” or any of the divine titles (e.g., Yahweh; Adonai) and the persons, that is, the Father is “God” but so is the Son and Spirit. However, in many key “creedal” texts in the New Testament (e.g., 1 Tim 2:5 [discussed below]), there is a distinction, not just between the persons of the Father and the Son, but also between “God” and the Son, which is very non-Trinitarian. This is the case in John 17:3. The Greek reads:
αὕτη δέ ἐστιν ἡ αἰώνιος ζωὴ ἵνα γινώσκωσιν σὲ τὸν μόνον ἀληθινὸν θεὸν καὶ ὃν ἀπέστειλας Ἰησοῦν Χριστόν.
"Now this is life of the age to come that they may know you the only one who is the true God and the one whom you sent, Jesus Christ" (my translation).
The title, τον μονον αληθινον θεον (“the only one who is the true God”), is predicated upon a single person, not a “being” composed of three “persons” (however one wishes to define “person”), and such is predicated upon the singular person of the Father, with Jesus himself distinguishes himself in John 17:3 from “the only true God.” Absolutising this verse, this is a strictly Unitarian verse as only a singular person is within the category of being the “only true God.” However, in Latter-day Saint theology, “God” is a multivalent term, something Trinitarianism cannot allow when speaking of (true) divinities. That this is the Christological model of “Biblical Christianity” can be seen in many places, such as Heb 1:8-9:
But unto the Son he saith, Thy throne, O God, is forever and ever; a sceptre of righteousness is the sceptre of thy kingdom. Thou hast loved righteousness, and hated iniquity, therefore, God, even thy God, hath anointed thee with the oil of gladness, above thy fellows.
This is an important pericope for many reasons—this is one of only a few places in the New Testament where Jesus has the term "God" (Greek: θεος) predicated upon him (others would include John 20:28 and probably, based on grammar, Titus 2:13 and 2 Pet 1:1], and yet, post-ascension, Jesus is differentiated, not simply from the person of the Father (ambiguously tolerated in Trinitarianism), but a differentiation from God (literally, the God [ο θεος]), something not tolerated in Trinitarianism. This can be further seen in the fact that this is a "Midrash" of Psa 45:6-7, a royal coronation text for the Davidic King, of whom Jesus is the ultimate fulfillment (cf. 2 Sam 7). Both the Hebrew and the Greek LXX predicates "God" upon the king, and yet, there is a God (in the case of Jesus, God the Father) above him. The LXX reads the same as Hebrews; the Hebrew literally reads "elohim, your elohim" (alt. "God, your God" [ אֱלֹהִ֣ים אֱ֭לֹהֶיךָ (elohim eloheyka)]
Another text that poses similar problems to Trinitarian dogma is Eph 4:5-7, which reads:
One Lord, one faith, one baptism, One God and Father of all, who is above all, and through all, and in you all. But unto every one of us is given grace according to the measure of the gift of Christ.
In this pericope, εἷς, the cardinal number meaning 1 (and no, it and the Hebrew equivalent [אֶחָד] does not mean "plural one" or other such nonsense! For a refutation, see my article here, or Anthony Buzzard on אֶחָד here), and is predicated on the number of how many Lords, baptisms, and Gods and Fathers Christians have--numerically, one. Furthermore, "God" is equated, not with the Triune being or upon three persons, but one, God who is the one (again, εἷς) Father. Verse 7 distinguishes between, not just the Father, but the One God (εἷς θεὸς). Again, this is not consistent with much of Trinitarian formulations.
The Ephesian text is paralleled in Mal 2:10, where our having "one father" is paralleled with our having "One God) (i.e., God the Father, not the Tri-une being):
That a single person is in view is strengthened by the fact that "created" is in the third person singular (בְּרָאָנוּ/ἔκτισεν)
The Ephesian text is paralleled in Mal 2:10, where our having "one father" is paralleled with our having "One God) (i.e., God the Father, not the Tri-une being):
Have we not all one father (אָב אֶחָד/πατὴρ εἷς)? Hath not one God (אֵל אֶחָד/θεὸς εἷς) created us?
That a single person is in view is strengthened by the fact that "created" is in the third person singular (בְּרָאָנוּ/ἔκτισεν)
For further instances of the subordinationist Christology in Paul (and John), see here for a discussion of John 17:11-12 and Phil 2:5-11.