Christians always think that Muslims are worshiping a different God from Christians. They always ask Muslims: “Who is Allah whom you worship?” Actually Muslims worship the same God Christians worship. Allah is the God of Adam, Noah, Abraham, Moses, David, Jesus and Prophet Muhammad (Peace be upon them all). Allah is God whom the prophets taught people to worship. This is what the Quran says and confirms when it orders us to believe in all prophets and tell the people of the book (Jews and Christians) that we serve the same God.
Allah is actually composed of two Arabic words “Al Elah”, which means “The God”. The word “Elah” has been used in Daniel 2:20 referring to God in Hebrew. In Aramaic, the word used for God is Alaaha, which is very similar to Allah. This word has been used in the “Passion of the Christ” movie referring to God. Arab Christians use the word “Allah” referring to God and the word “Allah” is always written in the Arabic Bible referring to God. So actually when we ask: “Who is Allah?” The simple answer should be God of Jews and Christians as shown in Aramaic and in Arabic Bible and as the word “Elah” is referred to God in Hebrew.
There is a common misconception among Christians that Allah is the moon god used to be worshipped by some pagans before Islam. Actually there is no proven evidence that there were pagans who worshipped a moon god and called him Allah. Actually the Quran is clear about not worshipping the sun or the moon and orders Muslims not to bow to the sun or to the moon but to Allah who created them.
Christians may point out that the crescent is the symbol of Muslims and this is shown on some Muslim flags and on the minarets of the mosques. But actually there is no evidence from the Quran or from what Prophet Muhammad said telling that crescent is the symbol of Islam. All what the Quran says about crescent is that it is a reference for determining the beginning of the month and it is used in Islamic calendar. For sure that doesn’t give crescent any sort of veneration, but it is just a tool. Using the crescent as a symbol was an Ottoman tradition that was first used on their flag. But nowhere did the Quran or the Sunna tell us to use it as a symbol.
Another common misconception regarding that “moon god” argument is that Arabs before Islam used to pray to 360 idols at Kaaba and consider Allah as their supreme God. Actually we must look at the history of Arabia to understand this point. When Ishmael came to Arabia, he taught his descendants to worship Allah who is God of his father Abraham and God of all prophets. Ishmael and Abraham built the Kaaba which is the house of God so that people worship Allah. The Kaaba is the house of Baca as mentioned in Psalm 82:6 and in Holy Quran 3:96. Ishmael told his descendents who are actually Arabs to worship God alone. Arabs kept on worshipping God only for some time, and then they began to worship idols and turn away from God as what happened with the Israelites. Although they acknowledged that Allah is the Lord who created us and who manages the universe, they associated other gods with Him and directed their worship towards them. Prophet Muhammad came to correct their belief and restore them back to the right belief in God and in all prophets. So simply it is not that Islam took the name Allah from Arab pagans, but actually Islam came to restore people to worship Allah alone who is God of their ancestors Abraham and Ishmael and reject the gods whom pagan Arabs associated Allah with. So when a Christian asks: “Who is Allah?” the answer shall be: “Allah is my God, your God and God of all prophets.”