Hey @selah, welcome to Uncommon Pursuit! I think you’ve asked a really important question!
I can’t pretend I’m an expert on explaining the Trinity. Some days I get it, and other days I’m wrestling with another question about how it actually works!
I happen to be reading a book on the Triune nature of God at the moment, called ‘The Good God: Enjoying Father, Son and Spirit’ by Michael Reeves. I highly recommend it, as it digests this difficult concept in very lay terms, and it’s not a thick academic tome either! If I could, I’d probably just put the whole book in quote marks below, but since that’s probably breaking copyright, I’ll quote him in places!
What struck me in Reeves’ argument for the Trinity is that if you take away all the things that God does (create, heal, discipline, judge…) and simply look at who he is, you get to the basic fact: God is love (1 John 4:7).
For God to be the very essence of love, not just love as a verb, He has to have someone to love. If God is unchanging, yesterday, today and forever, He must always have had someone to love. Reeves goes on to give examples of gods in other cultures who were at the start of creation before there was anyone else to love.
Imagine a god who is the origin and cause of everything else. He brought everyone and everything into being. Now before he caused anything else to exist, this god was all alone. He had not made anyone yet. Solitary for eternity, then. And so, for eternity this solitary god can have had nobody and nothing to love. Love for others is clearly not his heartbeat. Of course, he would probably love himself, but such love we tend to think of as selfish and not truly loving. By his very nature, therefore, this lonely, single god must be fundamentally inward-looking and not outgoingly loving. Essentially, he is all about private self-gratification. That, therefore, is the only reason why he would create.
The author addresses this in respect to Islam:
There is a fascinating tension at just this point in Islam. Traditionally, Allah is said to have ninety-nine names, titles which describe him as he is in himself in eternity. One of them is ‘The Loving’. But how could Allah be loving in eternity? Before he created there was nothing else in existence that he could love (and the title does not refer to self-centred love but love for others). The only option is that Allah eternally loves his creation. But that in itself raises an enormous problem: if Allah needs his creation to be who he is in himself (‘loving’), then Allah is dependent on his own creation, and one of the cardinal beliefs of Islam is that Allah is dependent on nothing.
Therein lies the problem: how can a solitary God be eternally and essentially loving when love involves loving another?.. Such are the problems with non-triune gods and creation.
The Trinity is the only way to answer this problem of God eternally loving another without needing creation to fulfil his nature; after all, God isn’t needy or he isn’t much of a God! Father, Son and Spirit can depend on each other to fulfil the identity of love and still be independent of everything.
The Oneness of the Trinity is therefore exactly demonstrated in this idea of an eternal, on-going love between Father, Son and Spirit. I suppose the closest human analogy is marriage : 2 people, 1 flesh. A husband and wife have a oneness about them.
Everything changes when it comes to the Father, Son and Spirit. Here is a God who is not essentially lonely, but who has been loving for all eternity as the Father has loved the Son in the Spirit. Loving others is not a strange or novel thing for this God at all; it is at the root of who he is.
The other thought I had is that as humans it is natural to consider ‘oneness’ to mean just ‘one person’. Maybe we need to be ready to consider that any god worth our worship might exceed our natural understanding of neat and tidy mathematics? Our One God is made of Three Persons, wrapped up in this eternal love that overflowed into creation, not because God needed creation for love, but because the love within the Trinune God is so over-abundant, that it brings God joy to pour it out, like a fountain into all creation. I often feel that if we are able to fully comprehend God then He must be a fairly small God. Perhaps simplicity isn’t always a satisfactory target?
Finally, have you read Nabeel Qureshi’s book ‘No God but One’? He was a devout Muslim who eventually became Christian. He puts forward some interesting theological mind challenges regarding the identity and nature of the true God, helpfully addressing both Muslim and Christian perspectives. It would be worth a read if you haven’t already.
I pray that you will have really fruitful conversations with your Muslim friends!