“When My servants ask thee concerning Me, I am indeed close (to them): I listen to the prayer of every suppliant when he calleth on Me: let them also, with a will, listen to My call, and believe in Me: that they may walk in the right way.” (al-Baqarah 2:186) Or “Verily, I am Allah: there is no god but I: so serve thou Me (only), and establish regular prayer for celebrating My praise.” (Taha 20:14) or “But, without doubt, I am (also) He that forgives again and again, to those who repent, believe, and do right, who, in fine, are ready to receive true guidance.” (Taha 20:82) or see another example where both pronouns are used side by side, “Before them the People of Noah rejected (their Messenger): they rejected Our servant, and said, “Here is one possessed!” and he was driven out. Then he called on His Lord: “I am one overcome: do Thou then help (me)!” So We opened the gates of heaven, with water pouring forth. And We caused the earth to gush forth with springs. So the waters met (and rose) to the extent decreed. But We bore him on an (Ark) made of broad planks and caulked with palm-fiber: She floats under Our eyes (and care): a recompense to one who had been rejected (with scorn)! And We have left this as a Sign (for all time): then is there any that will receive admonition? But how (terrible) was My Penalty and My Warning? (al-Qamar 54:9-16)
See also some verses where the first person plural is used: “We have, without doubt, sent down the Message; and We will assuredly guard it (from corruption).” (al-Hijr 15:9) or “We created not the heavens, the earth, and all between them, but for just ends. And the Hour is surely coming” (al-Hijr 15:85) or “And among His Signs is this: thou seest the earth barren and desolate; but when We send down rain to it, it is stirred to life and yields increase. Truly, He Who gives life to the (dead) earth can surely give life to (men) who are dead. For He has power over all things.” (Fussilat 41:39). Or “Already has Our Word been passed before (this) to Our Servants sent (by Us). That they would certainly be assisted. And that Our forces, they surely must conquer. So turn thou away from them for a little while. And watch them (how they fare), and they soon shall see. Do they wish (indeed) to hurry on our Punishment? But when it descends into the open space before them, evil will be the morning for those who were warned (and heeded not) (al-Saffat 37:171-177). There are many other examples.
Message, I dun think you have read the whole thing. Notice the singular and the "We" verses. Is God that careless to use a singular sentence and the "We" sentence in Quranic verses? If there's trinity in Quran, why is there still a singular sentence?
For a better explanation :
Two types of plural:
In several languages, there are two types of plurals, one is a plural of
numbers to refer to something that occurs in a quantity of more than one.
The other plural is a plural of respect.
In the English language, the Queen of England refers to herself as We
instead of I. This is known as the royal plural.
Rajiv Gandhi, the ex-Prime Minister of India used to say in Hindi Hum
dekhna chahte hain. We want to see. Hum means We which is again a royal
plural in Hindi.
Similarly in Arabic, when Allah refers to Himself in the Quran, He often
uses Arabic word Nahnu meaning We. It does not indicate plural of number
but plural of respect