Very interesting question, and this is my initial reaction to thinking through this…
First off, I don’t this this is Abdu’s personal argument, but instead Abdu articulating what Muslims believe in general. (I could be wrong, so please correct me if I am!)
I think a fundamental difference is what (very generally) Muslims and Christians believe about their holy book. As I understand it, a tenet of Islam is that the Quran is a direct transmission of Allah’s word to Mohammed, while the Bible is the ‘inspired’ word of Jawheh…though, of course, in the prophets, we have the direct transmission of, ‘thus says the LORD’. So maybe decide about how you would articulate the Christian tenet of ‘inspiration’?
It has also struck me that Islam is a religion that greatly values power and strength, so what interests me is what they consider ‘weakness’. What does the Judeo-Christian God value that Allah does not? It seems that clarity of message is what comes up in this instance. But is that an actual weakness? I mean, numerous Christians throughout the centuries have called into question God’s seeming lack of clarity, but what does God’s ‘hiddenness’ mean? (There’s a massive rabbit trail of philosophy and theology for you to enter there!)
I always end up with more questions that answers these days, but I think that’s the exciting part about you having the conversation with your Muslim friend. You guys generate and explore these questions together and that’s what grows us! Praying for you and your friend.