I differ with those who believe that Jews and Muslims worship the same God. Ishmael and Isaac were both sons of Abraham through different mothers. God saved the lives of Sarah’s maid Hagar and her son Ishmael after they had been expelled by Abraham and were about to die of thirst in a desert.
However, the step-brother relationship is not the question; the question is whether the god that Mohammed introduced to the world in AD 625 was in fact the God of Ishmael or instead a god chosen by him from among other deities.
An objective comparison between the character of Allah as revealed in the Quran and the God of Abraham as revealed in the Bible makes a very clear distinction between the two. God blessed the child Ishmael and promised his mother Hagar that he would become twelve tribes (the same number of tribes as those who would come through Jacob ( later renamed Israel).
What a blessing it would be if the Arabs, the offspring of Ishmael, were to reconnect with the offspring of Isaac and the God of Abraham, who is the patriarch of both. Such recognition and mutual acceptance between both descendants would renew an important ancient relationship, and through it, the prized blessing on both of the One True God.
Half-brothers in ancestry but full brothers as new creations through the shed blood of the Lord Jesus and sharers under the Fatherhood the One True God.