How do Trinitarians explain the almost exclusive use of singular pronouns to refer to God in the Bible?

The pronoun “ us “ depends upon how a person understand and self interpret the bible.

St. Ignatius in his epistle to the Philippians expanded the unity of the three divine persons.

Ante Nicene Fathers by Philip Schaff, p. 318. Chapter II.—Unity of the three divine persons.

There is then one God and Father, and not two or three; One who is; and there is no other besides Him, the only true [God]. For “the Lord thy God,” saith [the Scripture], “is one Lord.”824 And again, “Hath not one God created us? Have we not all one Father?825 And there is also one Son, God the Word. For “the only-begotten Son,” saith [the Scripture], “who is in the bosom of the Father.”826 And again, “One Lord Jesus Christ.”827 And in an- other place, “What is His name, or what His Son’s name, that we may know?”828 And there is also one Paraclete.829 For “there is also,” saith [the Scripture], “one Spirit,”830 since “we have been called in one hope of our calling.”831 And again, “We have drunk of one Spirit,”832 with what follows. And it is manifest that all these gifts [possessed by believers] “worketh one and the self-same Spirit.”833 There are not then either three Fathers,834 or three Sons, or three Paracletes, but one Father, and one Son, and one Paraclete. Wherefore also the Lord, when He sent forth the apostles to make disciples of all nations, commanded them to “baptize in the name of the Father, and of the Son, and of the Holy Ghost,”835 not unto one [person] having three names, nor into three [persons] who became incarnate, but into three possessed of equal honour.

824 Deut. vi. 4; Mark xii. 29. 825 Mal. ii. 10. 826 John i. 18. 827 1 Cor. viii. 6. 828 Prov. xxx. 4. 829 i.e., “Advocate” or “Comforter;” comp. John xiv. 16. 830 Eph. iv. 4. 831 1 Cor. xii. 13. 832 Eph. iv. 4. 833 1 Cor. xii. 11. 834 Comp. Athanasian Creed. 835 Matt. xxviii. 19. 318

How do Trinitarians explain the almost exclusive use of singular pronouns to refer to God in the Bible?

For Trinitarians there is one God (singular) in three Divine Persons (plural). The use of a singular or plural pronoun will depend on the circumstances in which such pronouns are employed.

There is but one God. The singular pronoun is correct.

There is but one Trinity. The plural pronoun is also correct.

Some Christians may believe that the plural pronoun of God refers to Himself and includes the heavenly assembly of angels, but Trinitarians refutation of this thought is through their belief in the Sacred Trinity.

Some believe that in Genesis 1:26 God refers to Himself and includes the heavenly assembly of angels, as in Job 1:6; 1 Kings 22:19–20; and Psalm 89:5. However, this theory falls apart because nowhere in Scripture does God say that the angels are made in His image or likeness. Another hypothesis suggests that the plural form is used to convey dignity and splendor, a language device called “plural of majesty.” Others chalk up the plural language to a technique known as “plural of deliberation,” used when a speaker consults with himself as the Lord does in Isaiah 6:8: “Then I heard the voice of the Lord saying, ‘Whom shall I send? And who will go for us?’”

The conviction of the Early Church Fathers was that Elohim’s statement, “Let Us make man in Our image,” communicates a complex and unified expression of the Trinity. The doctrine of the Trinity holds that God is One in three Persons: God the Father; God the Son, Jesus Christ our Savior; and God the Holy Spirit. Here in Genesis 1:26, the “Us” and “Our” indicate God the Father speaking in the fullness of His divine creative power to the Son and the Holy Spirit. A similar conversation among the Godhead is seen in Genesis 3:22: “And the LORD God said, ‘The man has now become like one of us, knowing good and evil.’”

Only humans are uniquely created in the image and likeness of God, distinguishing them from all other earthly beings. We were made like Him so that we could be in relationship with Him—the one and only triune God. - What does it mean when God said, “Let Us make man in Our image” (Genesis 1:26)?

The answer of the Nicene Creed - and I think also of the Holy Scriptures (1 Corinthians 8:6, 1 Timothy 2:5, John 17:3) - is that there is "one God, the Father", and that his only-begotten Son is "true God of true God, begotten not made, of one essence with the Father". The Son can properly be spoken of as God (John 1:1, John 20:28, 2 Peter 1:1, Titus 2:13) because he is of one essence with the Father, and is the "exact representation of his being" (Hebrews 1:3). The Holy Spirit "proceeds from the Father" (John 15:26; also Nicene Creed) and also shares the Father's essence and divinity. Though the Son and the Spirit share the Father's essence, they are distinct persons, not modes or manifestations of the Father.

In the New Testament, the term "God" usually references the Father (not the Trinity as a whole), and "Lord" usually references the Lord Jesus Christ (see again 1 Cor 8:6).

Trinitarianism does not turn on plural or singular pronouns but on scores of passages which establish the divinity of the Son and the Spirit.

The above understanding is not novel, but - to the extent that I have explained it correctly - is the faith of the ancient church, as well as that of the Catholic, Orthodox, and various other denominations.

EDITED TO ADD: The Nicene understanding is also called "the monarchy of the Father" - a potentially confusing term, but check the following link for more explanation:

https://cbtseminary.org/whos-tampering-with-the-trinity-4/

And here for a very detailed, scholarly, and expansive treatment:

https://beaubranson.com/monarchyofthefather/

Isaiah 44:6. “This is what the Lord says, He who is the King of Israel and his Redeemer, the Lord of armies:

‘I am the first and I am the last, And there is no God besides Me.

The Hebrew word for One is echad and also means compound unity. Isaiah 44:6 starts out compound and ends in unity. Redeemer = Messiah
He is ONE
He didn't need to say He was God. It was understood.
John 10:33 That's why they killed Him.

Who is Lord God Almighty in Rev 11:17? Its not the Father coming back.

How do trinitarians explain the heavily weighted use of singular pronouns to refer to God in the Bible, if God is 3 persons?

In School (Roman Catholic religious education) we were told in the first grade that you have to compare this to a principle that is also observable for nearly all persons and objects:

• A house consists of multiple rooms - although it is one single house
• A tree consists of leafs, branches, a trunk and a root - although it is one single tree
• A human body consists of a head, arms, legs ... - although it is one single human body
• ...

You'll find this principle nearly everywhere in the nature:

One single thing consists of multiple parts...

So there is no contradiction between being something singular (e.g. a single house) and consisting of multiple parts (e.g. multiple rooms).

The same principle applies to the trinetarian idea of God.

The Christian who experiences the presence of the Holy Spirit within himself, that is to say within his own spirit, experiences the fact of unity of spirit - that unity of person which joins himself with the Divine Person of the Holy Spirit.

... he that is joined unto the Lord is one spirit. [1 Corinthians 6:17 KJV.]

Thus, without (by record) and within (his own self) he is aware of both the fact and the experience of 'drinking in to one Spirit', 1 Corinthians 12:13, in common with all who have such unity and fellowship with the Deity.

This experience does not result in a division of spirit within, for the Holy Spirit dwells within one's own spirit. True, there may be turmoil but the dichotomy is betwixt one's spirit and one's flesh. Paul makes clear in Romans 7 that 'it is no more I that do it' (the sin that is unwilling) but 'sin that dwells within me'. That is to say it is no more my spirit that does it, but sin that is in the flesh.

I say again, the dichotomy is not between two spirits within but is rather between a union of spirit and the flesh.

For sin dwells in the flesh. And the Spirit lusts against the flesh and the flesh lusts against the spirit, Galatians 5:17.

Thus the Christian who experiences such a unity of spirit with God himself, understands that God is one. That is to say God is one Spirit. And understands that when Jesus says 'I and the Father are one' he is saying, in effect, 'I and the Father are one Spirit.'

The verb is plural. But the union is singular. 'They' (plural) are 'one' (singular).

For Jesus also says that 'God is Spirit' or, to more precisely express the Greek, he says 'Spirit, the God' conveying an equivalence, John 4:24, πνευμα ο θεος [TR undisputed].

The reason I say all this is to convey the foundational truth that spirit may dwell in union with spirit. This is a fundamental concept to grasp.

And if spirit dwell in union with spirit, then that spirit is one.

As Jesus says, 'I and the Father are One', John 10:30, εγω και ο πατηρ εν εσμεν [TR undisputed].

So it is not surprising, and it is not difficult to grasp, that Divine Nature is expressed as a singular since the union of Divine Person is so perfect, so intimate, so agreeable, so delightful in amiability, so singular in purpose, so adamant in unanimity - that it is expressed as a singular.

This union could never be expressed under law, or prior to the coming, in flesh, of the Son of God. It is he who declares the Father. Prior to this revelation there were but hints, brief manifestations, allusions, prophecies, but the reality and the fact was not made known until the coming of Jesus Christ and even then, not publicly declared until his own resurrection, Romans 1:4, declared that he is the Son of God and, thus, revealed the Father.

For God was a father to Israel it is true, but that was only as Creator, only as a privilege to a chosen nation upon earth, chosen out of other nations as a means to give testimony to the coming New Testament. It was no more than that.

But the revelation of the Father in the New Testament, upon the resurrection of Jesus Christ, the Son of God, is that of a begetting Spirit and an indwelling Spirit and is the revelation of a union of Spirit, that as far transcends the temporary demonstration of coming reality in Israel as does the heaven transcend the earth.

However, note that when considered as individual persons, the plural is used :

If a man love me, he will keep my words: and my Father will love him, and we will come unto him, and make our abode with him. [John 14:23 KJV],

ελευσομεθα (we will come) and ελευσομεθα (we will make) are both first person plural. But μονην (an abode) is singular. Two persons, one abode, within the one spirit of him who loves the Lord Jesus and keeps his word.

If, now that he is resurrected and ascended, Jesus Christ, the Son of God, is going to come and the Father, also, is going to come and they (plural) are going to make an abode (singular) with me, then God in two persons is going to abide with me, in a single abode, within my own spirit.

Thus is experienced, in Spirit, the fact of Divine Persons dwelling in a perfection of unity, within the born again believer.

The use of the singular is not exclusive, as here is exemplified.

If I might put this in simple language, the Trinitarian position is that there is one God, and he exists in three persons.

It is entirely correct, grammatically and philosophically, to refer to God in the singular pronoun. He is One. This is true even if he consists of Father, Son and Holy Spirit.

It is worth pointing out that the English language (and any other human languages) were not designed to describe a being who is at the same time singular (one God) and also plural (three persons). Any choice of language or pronouns is going to be to some extent inaccurate.

Even if this were not the case, the singularity of the pronoun is not an indication against the Trinity. In English group nouns take the singular case: "There is a committee. It reviews applications." "It" is a singular pronoun, and while in English it is gender-neutral, that is not the case for all languages. Similarly: "I joined the team. It plays football.". I believe Hebrew and Greek take the same approach.