The fact that several religions speak about one God does not show that they teach the same religion. It shows that they may share remnants of truth, while still making different and competing claims about God, revelation, sin, salvation, and the final prophet.
Why the objection is appealing
The argument has real force at first glance. Judaism, Christianity, and Islam are historically connected, affirm one Creator, honor many of the same prophets, and arose among peoples divided by language and culture. It can therefore seem arrogant to say that one is true while the others are mistaken. Perhaps God intentionally gave humanity different religious paths, and perhaps even Muhammad (PBUH) was a prophet within a wider religious pluralism.
History also teaches caution. Greek religion was once practiced sincerely, with temples, priests, and public rituals; later generations called its gods mythology. Why should Islam assume that its present confidence will not look equally naive in the future?
Shared origin does not mean identical truth
Islam does not deny that earlier communities received revelation. It teaches that all prophets called people to worship the one God, but that later human beings disputed, altered, or misinterpreted parts of what they received. Thus, the common ground is evidence of a shared prophetic origin, not proof that every later doctrine is equally valid.
Say, "We believe in Allah and what has been revealed to us and what was revealed to Abraham, Ishmael, Isaac, Jacob, and the Descendants, and what was given to Moses and Jesus and what was given to the prophets from their Lord. We make no distinction between any of them, and we are Muslims in submission to Him."
Quran 2:136
The differences are not minor differences of vocabulary. Christianity's doctrines of incarnation and Trinity, Judaism's rejection of Jesus and Muhammad (PBUH), and Islam's insistence on God's absolute oneness cannot all be true in the same sense. Saying they are "different languages" avoids rather than resolves these contradictions.
What religious diversity actually proves
The Quran acknowledges that human diversity in language and culture is part of God's creation:
And among His signs is the creation of the heavens and the earth and the diversity of your languages and your colors. Surely in this are signs for those of knowledge.
Quran 30:22
It also says that peoples and tribes exist so that they may know one another, not so that truth becomes unknowable:
O humanity, indeed We created you from male and female and made you peoples and tribes so that you may know one another. Surely the most noble of you in the sight of Allah is the most righteous of you.
Quran 49:13
Diversity explains why people encounter different beliefs; it does not establish that all beliefs are true. A sincere person can still be mistaken. Islam's claim is tested through the Quran's message, its conception of God, its preservation, its historical claim, and the life and teaching of the Prophet Muhammad (PBUH). Commitment is not arbitrary merely because alternatives exist.
Does history make certainty impossible?
The disappearance of Greek religion shows that a religion can lose social influence. It does not show that it was once true, nor that every surviving faith is destined to fail. Predictions about Islam should be assessed by evidence, not by the mere possibility of future change.
Islam does not promise that every person will be forced into certainty. It asks for honest reasoning, moral seriousness, and openness to revelation. Religious pluralism may explain disagreement, but it does not remove the question of which claim about God is actually true.