Personally, I see my Catholic faith as an extremely coherent way of explaining reality and life in its diverse facets. Truth be told, prayer and the attempt to foster a personal relationship with Jesus Christ have been a key factor in this coherency, but still I can never be sure whether the God I am praying to is the Trinitarian God or Allah of Islam.
So, I go to apologetics for reassurance. There have been eucharistic miracles down the centuries, there are the incorruptibles, there are the mystics, those with the stigmata, the arguments for the resurrection, and other fallible aesthetic experience I have had which leads to the likely conclusion that God is indeed love.
But I’m not bigoted enough to say that the evidence I have seen for Catholicism is the monopoly of all evidence for faith with regards to every person. This is the way I see history, philosophy, and logic, and thus for me it is within reason to make the elevated step towards faith in Christ. However, I can only assume that every person of every other religion goes through the same process. Certainly it would be non-sensical to believe something if your reason objected to it (the sacraficium intellectum of Thomas Aquinas).
So, then, there must be a reason why the Islamic faith does not view Jesus as God. It seems from people’s responses that it is because the NT is invalid, whether by a purposeful deceit or extreme ignorance on the part of the authors.
Perhaps Lewis should have rephrased to say, “Given the Gospel accounts as a historical record, then Jesus was either lord, liar, or lunatic.”