Trinitarian argument is based on pronouns proving "person". It is their assertion there are three persons. It is Oneness basically that asserts One God became the Son and could therefore refer to God as a "he" as though God is someone other than the Son.
Zec 12:10 And I will pour upon the house of David, and upon the inhabitants of Jerusalem, the spirit of grace and of supplications: and they shall look upon me whom they have pierced, and they shall mourn for him, as one mourneth for his only son, and shall be in bitterness for him, as one that is in bitterness for his firstborn.
Notice in this verse the speaker is "I" and says "they shall look upon ME, whom they have pierced"?
Then notice how the pronouns shift to the second person? And they shall mourn for him.
The First personal speaker became a second personal speaker in the same context.