It is common to see Christians use the 1+1+1=1 equation to describe the trinity. Their intention is good, but I think utilizing this equation as an illustration of the trinity is misguided.
When we look at the equation we conclude that the trinity is irrational. All our lives we have known 1+1+1=3 not 1. But now we are instructed that there is a heavenly math of sorts where it equals 1.
I was sharing the gospel with a Muslim years ago at the University of Texas in Dallas. He said he could never become a Christian because the trinity was irrational. I shared with him that irrational was not the right word. Mysterious to be sure, but not irrational.
Irrational would mean we are saying God exists simultaneously as one Person and three Persons. Another irrational option would be to say God exists simultaneously as one Being and three Beings. But of course, Christians don’t believe either one of these things.
We do believe that God is one in His Being or Essence, yet three in Person. Each Person is fully God not 33.333% God. That is why you can’t conceptualize the trinity. It is indeed beyond our understanding, but that does not make it irrational.
I asked my Muslim friend if he could conceptualize everything about Allah. He conceded that he could not. He could not get his head wrapped around such things as God being uncaused or self-existent. I asked if he thought uncaused or self-existent would be irrational. “Not if He is God,” he replied. Of course, it would be irrational to say God is both self-existent and dependent on someone/thing else for His existence.
So let’s drop the 1+1+1=1 for the trinity. We don’t want to give the impression that belief in the Christian God is irrational. Mysterious and beyond our comprehension to be sure, but not irrational.