Actually, there does exist an essential difference between Islam and the other two Abrahamic religions and that difference has to do with the the “otherness” of Allah. In Islam, Allah is viewed as being so far above human capacity and goodness that he cannot be known even by analogy. There is nothing that compares with the goodness of Allah and nothing humans can do which would even be considered remotely “good,” except to do precisely what was revealed by the prophet Muhammad.
In Judaism and Christianity, the idea of man being created in the image of God – the Imago Dei – provides the grounds for a relationship with God. Natural moral law as grounded in the inherent goodness of each individual human person created in the image of God provides the link between man and God. God is merciful because of the essential God-created goodness present in each person made in his image. This connection between man and God is essential in Christianity – so essential that God could become fully human.
In Islam, that connection is non-existent because the goodness of Allah is infinitely beyond anything found in human persons. No thought, behaviour or act on the part of human beings besides submission to the will of Allah revealed through Muhammad can bring human beings any closer to God – not showing mercy, not obeying moral laws, not showing love or charity, only following the prescriptions of Muhammad.
Doing so will not get humans closer to Allah in any sense, merely that humans will be rewarded for doing so. There is no idea of coming to know and love God or being drawn to him as the Summum Bonum or beatific vision implies. There is only the reward of human pleasures for doing so.
There is, likewise, no objective means for determining right from wrong except what has been revealed to Muhammad by Allah. Reasoning, truth, morality or justice have no independent meaning which can be used as counterpoints by way of assessing whether Islam is correct or not on certain tenets or doctrines. These can’t be weighed or assessed in any objective sense. This is ruled out a priori by the contention that what has been revealed absolutely overrules every possible human objection or resistance by the simple fact that Allah is incomprehensibly above human thought or goodness such that any objections or interpretations on the part of human beings count for nothing.
These two talks by Robert Reilly provide an important perspective.
instituteofcatholicculture.org/islam-yesterday-today-tomorrow/