Every Jot and Tittle

I was reading in Jeremiah 20, this morning, when I noticed this strange language construction:

“The anger of the LORD shall not return until He have executed, and till He have performed the thoughts of His heart: in the latter days ye shall consider it perfectly.”  Jer. 23:20

Notice the auxiliary verb, HAVE used two times in this verse. 

The rule for using has vs. have depends on the personal pronoun that precedes it.  For pronouns in the first person (I and we) and some in the second person  (you, and they), use have.  If the pronoun is in the third person singular (he, she, or it), use has.

So why is that a big deal?  Well, I dunno; I just think that words mean things and I expect that God's Words were given with precision.  I’m not an expert on grammar and I know absolutely NOTHING about the Hebrew language or how this might read in the original text.  But it seems to me that the translators must have been smarter and more careful than me (or is it I?) and they probably took great pains to translate it accurately. 

[Incidentally, my spelling and grammar checker, Grammarly, will NOT let me get away with this.  It keeps insisting that God and I are wrong.]

It has been noted that there are many, many references, in every book of the Bible, to the tri-unity of God.  Could this be one of them that most of us might just overlook?  Think about it.  The reference is to God.  The pronoun is singular (He).  God is one god.  However, the auxiliary verb used (have) indicates a plural subject (a tri-unity), the Father, the Son, and the Holy Spirit.

Since God is One God in three persons, it seems that the language is and must be accurate; He (The One and only God) shall not return until He (the Father, Son, and Spirit) HAVE executed and performed the thoughts of His heart.”