At the core of Muslim and Christian beliefs is the doctrine of God. Christians believe God is Triune and the importance of this belief can be seen in the churches and universities that have Trinity in their name:
One belief that Muslims and Christians do not hold in common is Jesus’ death by crucifixion. Jesus’ death on the cross is central to Christianity. In fact, its importance can be seen in Christian art, Christian symbols, and the names of Christian institutions such as:
Christians are monotheists because Trinitarianism is a form of monotheism. Muslims reject Trinitarian monotheism. The Muslim belief is summarized by the word Tawhid (also spelled Tawheed or Tauheed). The first article of Islam (Shahada) begins, “there is no other god but God.”
It must be emphasized that both Christians and Muslims affirm monotheism. The issue is whether the Bible or the Qur’an gives the true explanation of monotheism: Trinitarian or Tawhid? This is important because Muslims often – such as Ahmed Deedat – misrepresent the doctrine of the Trinity. In fact, the Trinity rejected by the Qur’an is not Christian Trinitarian doctrine found in the Bible.
When Christians say: (1) The Father is God; (2) The Son is God; and (3) The Holy Spirit is God, we are identifying Who God is.
When we say: (4) The Father is not the Son; (5) The Son is not the Holy Spirit; and (6) The Holy Spirit is not the Father we are distinguishing the Father, Son, and Holy Spirit.
The seventh statement is the difficult one, “There is only one God.” The Greeks would say, “Zeus is god, Apollos is god, and Dionysius is god, and there are three gods” (polytheism). Christianity says, “The Father is God, the Son is God, and the Holy Spirit is God and there is only one God” (monotheism).
Trinitarianism is monotheism. The debate between Muslims and Christians is whether the monotheism of the Qur’an is true or whether the monotheism of the Bible is true. Does the Bible or the Qur’an present us with the one true God.
Christians believe that the Bible presents us with the one true God and that the Islamic form monotheism is one of its major weaknesses. As one Christian scholar notes:
Its [Islam’s] doctrine of God is the major weakness of Islam…Only a God who is triune can be personal. Only the Holy Trinity can be love. Human love cannot possibly reflect the nature of God unless God is a Trinity of persons in union and communion. A solitary monad cannot love and, since it cannot love, neither can it be a person…Trinitarian theology asserts that love is ultimate because God is love, because he is three persons of undivided loving communion (Robert Letham, The Holy Trinity, 446).