Try to get this round your head: Christians are idolaters and blasphemers in denial that they are idolaters and blasphemers.
For some reason, even as they incorporate the Torah into the Christian Bible and must know that the Ten Commandments include the prohibitions against idolatry and blasphemy, they lack the self-awareness and conceptual understanding to grasp that Christianity is the idolatrous worship of an executed blasphemer.
According to the Christian narrative, Jesus was executed for blasphemy and has been worshiped as the co-equal of the God of Israel who is also Allah for the best part of 2000 years.
When you point out the idolatry and blasphemy of Christianity, Christians either really do not understand or affect not to understand.
You would have thought they would recognise an idol when they see one, and recognise that what they do when they worship Jesus and Mary do is idolatry, but it seems they lack that requisite self-awareness and conceptual understanding of idolatry, which is a mortal sin according to Christianity.
When you finally make them grasp that they are idolaters and blasphemers, they shrug their shoulders and carry on.
Christians are a curious bunch, being atheists who pretend to believe in the absurdity that an executed blasphemer could be the co-equal of the supreme and eternal Abrahamic God who created the Universe.
If idolatry is indeed a mortal sin and Christianity is indeed idolatry, then they need not concern themselves that they will be going to heaven because their idolatry would damn them to the other place.
The Islamic heaven is a much pleasanter sounding place though.
https://en.wikipedia.org/wiki/Jannah
Restoring Truth, Logic and Morality with Secular Koranism