Many classical liberals are skeptical of religion because they are skeptical of all claims of power. And what power could be more indefensible than an invisible deity who hands down a set of moral demands, some of which many intelligent and sincere people have interpreted as prima facie illiberal, that are not open to question? Furthermore, many religious rules can seem like they come from power-seeking men, not a loving and just God. For those who care about human freedom, many religious traditions can seem oppressive in a similar manner to the state.
I do not agree with this critique.
The problem is that this critique only looks at one side of the equation. A religious worldview frequently holds that the highest moral law, that which commands universal respect, is antecedent to particular forms of human organization, including the state.
To me, classical liberalism is a limited worldview. It is not a grand metaphysical organizing principle for ordering all aspects of personal and social behavior. Rather, it is a system whose reach extends over only some social, moral, and political truths. Being a classical liberal is about recognizing (positively) that a huge portion of important human activities are not planned, and cannot be planned. It is also about recognizing (normatively) that it’s appropriate not to intervene coercively in many such orders, both because of the deleterious effects of such interventions, and because such interventions trespass against human dignity.

Classical liberalism is a limited worldview.”]
In addition, classical liberalism is not specific to any code of morality. Whatever the content of the moral law — and the vast majority of individuals, classically liberal or otherwise, believe in such a law — it transcends the particular truths of classical liberalism. This is not to say classical liberalism is immoral, or amoral; far from it! It simply means that there are rights and obligations whose definition and enforcement fall outside of the positive science of spontaneous orders, or the normative science of what conditions ought to underlie spontaneous orders, i.e. which political institutions we ought to live by, to the extent we can rationally choose them.

Classical liberalism is not specific to any code of morality.”]
Furthermore, even the religious traditions that exhibit (to those who are wary of it) an ancient and musty ecclesiology provide a bulwark against arbitrary coercion. Religious institutions are some of what Alexis de Tocqueville called “intermediary institutions”: the organizations and orders that comprise civil society, placing a buffer between the individual and the state, providing valuable communal needs, and embedding individuals in traditions that are both historically rich and open to new development. To paraphrase Edmund Burke, we need the ‘little platoons’ of civil society — including religious bodies — to make us fully human, and part of that is to protect us from the very, very big platoon in Washington, D.C. (or London, or Paris, or Beijing, or…)
‘No gods, no masters’ is a catchy slogan. But it is not a liberal one. If classical liberalism is about discovering the conditions requisite for human flourishing in an spontaneously developing society, then it has to account for what people demand from society — and by that, I just mean other people — at a deep level. One persistent demand is a sense of transcendence and ultimate truth. You can no more stamp this out than you can humanity’s tendency to ‘truck, barter, and exchange’.