If you actually empathize with a person who has different beliefs, for example, you'd realize that when somebody takes one religion, and changes it drastically, that the people with the earlier religion would not consider themselves to be worshipping the same god as the later religion. If Jews really thought Christians were worshipping the same god, they'd become Christians. If Jews or Christians really thought that Muslims were worshipping the same god, they'd all become Muslims. Islam came last, so of course they'd have the most up-to-date religion, right? Why would anybody keep the old ways if they actually thought Muslims worshipped their same god? They wouldn't. It makes no sense. Especially because the god in Islam seems quite different to the Christian god. Islam's religious text instructs the faithful to lie about their religion when it suits their needs, for example. Jesus described himself as the truth. Catholics, for example, believe that Jesus is god. Islam says that Jesus is only a prophet. That is a fundamental difference in who they believe is god. Their main religious figures couldn't be more different, either. The Jesus described in the Christian Bible was an educated Jewish holy man. Mohammed was an illiterate pedophile warlord. If a Christian thinks that their god is the same as Allah, then they just haven't thought about it. That is a belief of Islam, not Christianity.