...Or rather belief in the God of the Holy Bible only.
My emphasis was on the discernment of faith and belief. The Greek usage of PISTIS tends to be translated as one or the other in English or also as doctrine, but the same Greek word is used when referencing the mechanism of our thinking with respect to God.
We believe in God through faith in Christ. Same word is actually used for both faith and believe in the Greek. When arguments are made from a rationalistic perspective, addressing different faiths (doctrines) or different beliefs (objects of thinking) they tend to promote a perspective which actually is not through faith in Christ, but rather attempt to be a third party observing the thinking of all persons. That perspective, in and of itself isn’t through faith in Christ.
Ecumenical attempts to normalize religions into a common religion also fail to place simple faith in Him by His standards, which is through faith in Christ.
God doesn’t have to provide more than one mechanism by which man is able to have a relationship with Him. The Perfect relationship is already available and again only by Him.