Its usually more important what people mean by the words they use than the particular choice of wording they employ to communicate their ideas. Its easy to misspeak, or to phrase something in a way that does not perfectly capture the intended meaning.
When we come to the Bible, however, we come to something truly special. Because its authorship is divine, although written through human instrumentality, its authorship is not merely human, and thus is not subject to the kind of inaccuracies human frailty produces in our communication. The scriptures were inspired perfect and infallible, free from even the slightest error. Because of this, we can find a great deal of meaning even in seemingly minor details in the scriptures. Historically it has been noted that one such significant detail in the scriptures lies in the personal pronouns used to speak about the persons of the Trinity.
From very early on Christians have noted the great significance of the plural personal pronouns used in Genesis chapter one, for example. Among the earliest is the apostle Barnabas, who wrote:
“And further, my brethren: if the Lord endured to suffer for our soul, He being Lord of all the world, to whom God said at the foundation of the world, “Let us make man after our image, and after our likeness,”46 understand how it was that He endured to suffer at the hand of men. ” (Epistle, Ch 5.)
“For the Scripture says concerning us, while He speaks to the Son, “Let Us make man after Our image, and after Our likeness; and let them have dominion over the beasts of the earth, and the fowls of heaven, and the fishes of the sea.”” (Epistle, Ch 6)
You see the apostle noting the plurality of persons in the text, as God spoke to His Son, recognized on the basis of the pronouns scripture employs, and particularly on the significance of the number of the pronouns, namely, that they are plural and not singular. This significant detail was also noted by other notable theologians in the early church, such as Irenaeus, who wrote:
“He calls Him Wonderful Counselor, meaning of the Father: whereby it is declared that the Father works all things together with Him; as is contained in the first book of Moses which is entitled Genesis: And God said, Let us make man after our image and likeness. For there is seen in this place the Father speaking to the Son,  the Wonderful Counselor of the Father.” (Demonstration of the Apostolic Preaching)
Justin Martyr also made great use of these important details in his Dialogue With Trypho, A Jew, noting the detail that Holy Spirit used plural personal pronouns in Genesis one as evidence for the doctrine of the Trinity, as a proof that God did not create the world alone, but through His Son, a second person distinct from Himself. Justin wrote:
“And the same sentiment was expressed, my friends, by the word of God [written] by Moses, when it indicated to us, with regard to Him whom it has pointed out,409 that God speaks in the creation of man with the very same design, in the following words: ‘Let Us make man after our image and likeness. And let them have dominion over the fish of the sea, and over the fowl of the heaven, and over the cattle, and over all the earth, and over all the creeping things that creep on the earth. And God created man: after the image of God did He create him; male and female created He them. And God blessed them, and said, Increase and multiply, and fill the earth, and have power over it.’410 And that you may not change the [force of the] words just quoted, and repeat what your teachers assert,—either that God said to Himself, ‘Let Us make,’ just as we, when about to do something, oftentimes say to ourselves, ‘Let us make;’ or that God spoke to the elements, to wit, the earth and other similar substances of which we believe man was formed, ‘Let Us make,’—I shall quote again the words narrated by Moses himself, from which we can indisputably learn that [God] conversed with some one who was numerically distinct from Himself, and also a rational Being. These are the words: ‘And God said, Behold, Adam has become as one of us, to know good and evil.’411 In saying, therefore, ‘as one of us,’ [Moses] has declared that [there is a certain] number of persons associated with one another, and that they are at least two.”
The argumentation employed here is clear: because scripture uses personal pronouns that are plural and not singular, we must understand there to be multiple persons. The reasoning here is straightforward and rock-solid.
Unfortunately, many Christians today regard the detail of whether we use singular or plural personal pronouns for the persons of the Trinity together as a group as something unimportant. It is commonplace to see the Father, Son, and Spirit referred to together as “he” or “you”, with singular instead of plural personal pronouns.
Unfortunately, this is more than simply improper grammar: it implicitly teaches the false doctrine that the three real persons of the Trinity are actually a single person, which is semi-modalism. As we have seen, this is an unbiblical way to speak of the persons of the Trinity together, as scripture is careful to accurately portray reality by using plural personal pronouns for the persons as a group.
Instead of carelessly using language that implies false doctrine, we ought to use plural personal pronouns for the persons of the Trinity together, as scripture does. We must strive to be careful in the language that we use when speaking about God, His Son, and His Spirit. If we do so, instead of implicitly teaching something false about God, we will be implicitly declaring the truth of the Trinity, to the glory of God.