Yesterday, I wrote about what you might need to know about Islam before you share the gospel with Muslim people. You can read that post here. TL:DR: nothing. Just ask them what they believe and go from there.

However, in our frequent discussions together, certain topics happen to roll around again and again. How can Jesus be God? How can God have a son? Does the Trinity really make sense (and what is it actually)? The Bible has been changed, hasn’t it? All the old classics.

Some of these questions are extremely helpful. They’re often asked genuinely, in a spirit of having heard something about this and finding it a bit strange or hard to understand. Occasionally they’re asked a little disingenuously, waiting to spring little rhetorical traps of their own. In any case, it usually gives us a the opportunity to correct misunderstanding or to explain something quite core about what we believe.

One of the very interesting, and fruitful, lines of discussion we have found concerns the Trinity. It is usually asked with a sense of skepticism that it makes any sense at all. But in truth, when we explain what the Trinity is, it opens up some key conversations about the cross and specifically how God can legitimately forgive sin at all.

We affirm, along with our Muslim friends, that God is truly and properly loving as a property of his character. We also both affirm that he is merciful and just. But it is my contention that Islam has no explanation for whom Allah was loving before he created the world, thus making him needful of his creation and, by fulfilling a need in him to express his love, he therefore owes his creatures something. Similarly, there is no explanation for how Allah can be just and merciful at the same time. Islam insists that Allah simply forgives those he forgives, but has no explanation for how he can forgive in mercy and yet that, at the same time, be in any way just.

Christianity, by contrast, looks to the Trinity not as a problem, but as an answer to these very questions. God is totally sufficient in himself, enjoying the perfect loving relationship of Father, Son and Holy Spirit in eternity past. He has no need of his creation, but created us for his own good pleasure so that we might enter into that perfect loving relationship he enjoys in himself. Apart from the Trinity, there is only a needy God who needs us so he can express his love to something and fill up a need in him. A trinitarian God has no need of his creation, he was simply pleased to create it for his own pleasure.

Similarly, Christianity looks to the Trinity and the cross to explain how God can be both just and merciful. God does not simply ignore sin, but determines to take the penalty upon himself. Indeed, sin could not be paid for unless God himself takes the penalty. Only an infinite person can take an infinite punishment. If anybody else could be put forward, they would not be able to meet the full demands of God’s justice. They would not be able to bear an infinite punishment. It is only a Trinitarian God, who takes upon himself the infinite punishment, who can satisfy justice.

But more than that, the cross itself is the means by which God is able to show mercy to the sinner whilst satisfying his justice in himself on the cross. Yahweh does not simply show mercy and wipe the sin out. Nor does he enforce justice and show mercy to nobody. Instead, he comes himself and stands in place of his people so that he can show mercy to them whilst satisfying his justice by punishing sin in full in Jesus. It is both the doctrine of the Trinity and penal substitutionary atonement that provide any sort of explanation for how God can simultaneously be just and merciful without cancelling either out.

Allah, by contrast, simply wipes out sin capriciously. He determines who will be forgiven, for which there are seemingly no specific grounds, and then he wipes out the sin and forgets it ever occurred. But when he does so he foregoes justice altogether. He either shows his justice by punishing sin or he shows mercy by simply wiping sin out. But Allah has no mechanism for satisfying his justice and mercy at the same time. It is the Trinity that allows God to be both Just and merciful and loving as a property of his character. Yahweh is God because he is always these things and is not changed by things (like creation) outside of himself nor does he cease to show show these innate characteristics because, if he ever doesn’t show them, he isn’t being God. Allah simply has to pick and choose which of these characteristics he will show at any given time and which are in force depends upon the creation he has made and how he changes in relation to it.

I don’t mention these things as knock-down lines or clever traps to set in discussion with Muslim people. I mention them because they are helpful lines of enquiry to discuss with honest Muslim friends willing to talk these things through. You can compare the reality of what it means to believe in a Trinitarian God with what it means to believe in a Unitarian God and see which has more explanatory power in respect to the things we both agree God does and the characteristics he posseses.