There is a difference between a Muslim learning the truth about Christ and rejecting it, and a Muslim who has never learned about Christ.
It is the rejection of Christ, the turning away from the faith, a resolve to ignore the gospel that God finds unacceptable.
A Muslim who learns the truth about Christ and believes it, will no longer be a Muslim. He will be a Christian. Having the opportunity to learn of God’s all-encompassing love, this Muslim would have no choice but to believe on faith. It is this conversion that makes God rejoice.
We agree; but what will happen to the Muslim who never gets the opportunity? There have been many.