There are vast differences between the Holy God worshiped by Christians and the god revered by Muslims. They are not the same deity, although Muslims will have you believe otherwise. Here are 13 specific differences:
1. The Holy God is triune: the Father, Son, and Holy Spirit. (I Timothy 3:16)
Muslims reject this triune attribute. The Koran specifically teaches that the god of Islam can only be one, that is, just a god. He does not beget (chapter 112).
2. The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance. (II Peter 3:9)
The Muslim god leads some in the right way and to eternal reward, and leads others to do evil (or, into error) and subsequently to eternal punishment in hell.
3. Jesus died on a cross as a sacrifice for all sin, was buried dead, and resurrected by God through the power of the Holy Spirit. (Acts 5:30-31; Romans 8:11; I Corinthians 15:3-4, and many other Scriptures)
Muslims reject the substitutionary death of Jesus, His burial, and subsequent resurrection.
4. The Holy God is a God of grace, resulting in salvation. (Romans 5:15; Ephesians 2:8; Titus 2:11)
Muslims practice a works-based salvation as their hope to meet their god (in paradise), as taught by the Koran.
5. In the beginning was the Word, and the Word was with God, and the Word was God. Jesus is the living Word, and asserts the written Word. (John 1:1)
The Koran asserts itself above the Holy Scriptures, claiming to confirm that which was before it (the Old and New Testaments) and to explain the true meaning of the Holy Scriptures.
6. God alone gave the Holy Scriptures. (II Timothy 3:13-17)
The Muslim god, through the angel Gabriel, gave (or sent) the Holy Scriptures and the Koran, the latter to explain the Holy Scriptures.
7. Christians, as their name implies (sacredly and historically), do not deny the resurrection of Jesus and do expect a newly created body at their own resurrection. (Acts 11:26; II Corinthians 5:11)
Mohammed falsely accused Christians of denying the resurrection of Jesus while at the same time expecting their own resurrected bodies to be a new creation.
8. The Holy God will destroy all old things (that is, the heavens and the earth) at the end of time and will replace them with new. (II Peter 3:10-13)
The Muslim god will change the old heavens into new heavens and the old earth into a new earth. No mention is made of old stuff being destroyed or removed, and all things becoming new.
9. Angels worship God alone, and every created thing brings glory to God alone, including man. (Psalm 148; Hebrews 1:6)
The Koran teaches that the Muslim god ordered the angels to worship man when he created him. All but one (Satan, named Eblîs in the Koran) obeyed.
10. The Holy God does not tempt anyone. (James 1:13)
The Koran teaches that the Muslim god tempts people, even using the tactics of Satan to do so.
11. Jesus is our mediator. (I Timothy 2:5)
In Islam, the believer is his own mediator. Combined with works and almsgiving, this is how the Muslim god provides justice: accepting (or not) works and receiving (or rejecting) a self-justified claim of faith.
12. God prepared hell for the devil and his angels; subsequently, it is also the place of eternal punishment for unbelievers. (Matthew 25:41, 46)
The Koran teaches that the Muslim god prepared hell for unbelievers (infidels) of the Islamic faith.
13. For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life. (John 3:16)
The Muslim god does not love everyone, especially unbelievers.