A Question to God… “Aren’t you too mysterious for human beings to understand? Isn’t all of this just a great mystery that no one can comprehend?”
God Answers…“Let him who would boast take his boast in this, that he understands and knows me, that I am the LORD.” — Jeremiah 9:24
He himself testifies that his people should glory in that they “understand” and “know” him. The truth of how many compose the one God is not a mystery! It is knowable and is known to ancient Israel. Israel knows with absolute certainty: It is one! Moses says to the people:
To you it was shown so that you might know that the LORD, he is God; there is no other but him (Deut. 4:35).
The inherent difficulties in multi-person theology have driven some adherents to propose that the idea is simply a “great mystery” and can’t be understood. No one would argue with that assessment. Surely it would be an incredible mystery that in the Bible there is one affirming that only “he” is God while at the same time there are one or two other persons who share his Deity. This mystery, however, exists only for those proposing a multi-person God.
God is indeed the most spectacular being in the universe. He is truly unfathomable! We are finite — looking to the one who alone is infinite. Anyone who claims to fully comprehend him is surely deluded. Yet the most complex being in the universe is simple to understand in this regard: There is only one of him!
The fact that only one individual is God is directly, clearly and repeatedly addressed in the Bible. On the other hand, the contradictory concept that multiple persons are the one God is never directly stated or specifically addressed. That idea is a construct. If we are to believe in a mystery, it should be one that the Bible straightforwardly identifies and describes. Otherwise, how will we know that it is a mystery from God? How will we know that it is not simply confusion or misunderstanding that has been labeled “a mystery”?
Appeals for people to accept the idea of multiple persons as one God “by faith” also point to the extraordinary weaknesses of the theory. Why should we strain to have faith in a concept that must be labeled “a mystery” because it contradicts what the Bible forthrightly says? How many the one God is, is not a mystery at all. Why not let go of the contradictory multi-person “mystery” and embrace the clear revelation that only one individual is God? All of our faith toward God is due to the one of whom it is said, “There is no other but him” (Deut. 4:35). This too was Jesus’ belief ( John 17:3).
Let our appeal be that all would have the same faith in the same God that his people of old did. That faith is: Only one individual is God and “he” is all of God there is. Let us tell the world that our Father is perfect and that to imagine there are any other persons with Deity can only diminish him in the eyes of his own creation. It can only dilute the honor that is due him alone as God.
Gill, J. Dan (2016). It’s a mystery! In, The One: In Defense of God (pp. 207-208). Nashville, TN: 21st Century Reformation Publishing.
 Mystification is a rather desperate effort to defend the indefensible. Proponents of a multi-person God propose various ingenious “proofs” that God is multiple individuals. As those “proofs” fail, however, people often retreat to, “It’s a mystery that cannot be understood but must be believed.”
 For Jesus and his early disciples, only one individual is God. That one is the Father ( John 17:3; Eph. 4:6). Hence, there is no “mystery” spoken of in the New Testament about multiple persons being one God. This supposed mystery exists only for Christians in post-biblical times after the development of that incomprehensible notion. Designating the multi-person God idea as a “mystery” helps to obfuscate the fact that a theory which has been assigned paramount importance by post-biblical Christians is in reality both illogical and unscriptural. The post-biblical abuse of the concept of “mystery” can be contrasted with Paul’s use of the word (musterion) in his letters. Paul does not use the term to distract from logical or scriptural difficulties, but rather uses it to describe truths that were formerly hidden but now are known! He never identifies a multiple-person God as being one of those mysteries. Rather, Paul’s mysteries are truths about the Messiah and God’s blessing of salvation to people in all of the nations through this man (Rom. 5:15; 16:25–27, etc.).