Pastor Thabiti Anyabwile, a former Muslim, interacts with Miroslav Volf’s argument in his new book, Allah: A Christian Response, that one could practice Islam and be 100% Christian. Anyabwile also explains how the fundamental differences in doctrine—particularly regarding the nature of God in the Trinity—are irreconcilable:
Last year, Anyabwile released an excellent book on ministering to Muslims, The Gospel for Muslims (reviewed here). There, he offers three reasons for the necessity of holding fast to the doctrine of the Trinity:
First, because we are bound in humility to accept what God reveals of Himself. After all, we are creatures and He is the Creator; we are finite and He is infinite. Accepting and maintaining the Trinity as central to the Christian faith is to say to God, “I believe You—not others and not myself—as You reveal Yourself.” In short, believing and defending the Trinity is essential to genuine Christian faith and witness.
Second, because to deny the Trinity is to commit idolatry. Here the Christian and the Muslim come to irreconcilable differences. We may not maintain that God is one God in three Persons and at the same time accept that God is radically one with no persons in the Godhead as Muslims believe. That would be to accept a contradiction. And it would be to deny the revelation God gives of Himself, making an idol graven with the tools of our own imagination. God is jealous for His name. He calls His people to “worship [Him] in spirit and in truth” (John 4:24). Surrendering the Trinity turns us away from true spiritual worship of the only living God to idolatry.
Third, we must cling to the Trinity because apart from the Father, Son, and Holy Spirit, there is no possibility of eternal salvation. If we surrender the Trinity, or weaken our presentation of who God really is, we in effect deny the gospel. Each Person in the Godhead plays an essential part in redeeming sinners from judgment and bringing them to eternal life. (p. 37, Kindle edition)