I don't believe I ever said you couldn't be a real liberal without being a religious believer. Though I said something close to that. And by a "real liberal" I mean a liberal in the sense of the word which described the American liberal tradition, feeding the hungry, clothing the naked, healing the sick, visiting the prisoner, providing economic and legal justice to the orphan, the widow, the stranger living among us, creating and funding the best possible institutions that would do that with the power of government and non-governmentally, universal education, public universities, things like the GI Bill, etc. What Jonathan Edwards, of all people, you might think, described as "providing liberally" for the destitute among us.
I don't believe I ever said you HAD to be a religious believer to be that kind of a liberal. I certainly never said you had to be a Christian to be that kind of a liberal. What I said is that you couldn't be that kind of liberal on a reliably sustainable basis without having a real and solid belief in the metaphysical properties of people and other living beings which holds that they are endowed with rights by the simple fact of their character as living beings. In the most basic political manifestation of those inherent properties that define people as not being material objects but more than that, you have to believe something like the formulation in the beginning of the Declaration of Independence, that all people
... are created equal, that they are endowed by their Creator with certain unalienable rights, that among these are life, liberty and the pursuit of happiness. That to secure these rights, governments are instituted among men, deriving their just powers from the consent of the governed.
If you don't really, truly AND EFFECTIVELY, believe that, at the very least, your liberalism will never be grounded in anything that is durable and which is not liable to be abandoned for that favorite force of the British "Enlightenment", and the line of economic nonsense that comprises the neoclassical school of Friedman, self interest over the common good or due justice in any particular case.
The substitution of the various forms of Marxism as a materialist replacement of a firm belief in the metaphysical endowment of rights and moral obligations to observe those rights was one of the most disastrous and murderous experiments ever given to a philosophical idea in history. Marxist dialectal materialism forced itself into power, gave that idea a try and proved, in every case, that it was a horrific disaster.*
The alleged alternatives to Marxism, artificially and opportunistically charted on a false chart of political and economic philosophies, fascism, Nazism, market economics and even, I have come to believe, what goes by the imprecise name of "secular" capitalist economics and government, the vulgar materialism of consumerism have been and are a continuing disaster. I think the history of the late 19th and early 20th centuries have proved that materialistic philosophies, even when they pretend to serve as a substitute will always and inevitably end up with the opposite of what traditional American liberalism holds to be truths, the kind of which Jefferson gave a brief and far from complete list in that quote above.
If other systems of belief can give rise to a reliable and secure form of those truths, I don't know. I suspect that Judaism and Islam could, certainly in the current American context there are Jews and Muslims who are better on those than many people who profess Christianity. If other religions could, I don't know. I suspect that Buddhism might be able to and some strains of Hinduism - though not those which hold to the beliefs that gave rise to the infamous caste system.* It's possible that there are numerous religious traditions that could give rise to a government or politics that assert those truths. I doubt that any society where a majority of people held those attributes of people were not an endowment of their Creator or in some other way metaphysically and equally instilled in us could sustain egalitarian democracy for long.
I don't believe for a single second that atheist religious substitutes of "Humanism" or utilitarianism or, heaven help us, the "ethicists" who are always coming up with ways to justify infanticide and other means for getting rather stupid academics media time, will ever do anything but give excuses for moral depravity.
The attack on religion, gaining momentum in the post-war period and the pseudo-scientific attack on the mind and consciousness through asserting those are a mere epiphenomenon of material causation, the broadcast of the promotion of and seduction into the mindlessness of vulgar materialism and consumerism have had the greatest hand in producing the decline into Trumpery. Though I would say that the TV and movie and, now, internet seduction into self-aggrandizing consumerism has been the strongest force doing that. It has certainly hollowed out the religion of many who profess a Christianity at complete odds with the Gospel, the Prophets and the Law, the support of many such people for the neo-pagan materialism of Donald Trump has produced a disaster which rivals that of the imperial Roman Empire, whose religion was remarkably like the "Christianity" of the Trump supporters.
In the United States not only a revival of traditional American liberalism but of anything that aspires to egalitarian democracy depends on the revival of the kind of Christianity that is the cultural heritage of a large number of Americans who will not give that up. I think there needs to be a rigorous internal criticism of Christianity more profound than the atheist attack on it BECAUSE IT TAKES THE TEACHINGS OF THE JEWISH TRADITION AS BEING A PROFOUND EXPRESSION OF REALITY. I don't think Christianity should have ever stopped calling itself, on an individual or on a denominational and intra-denominational level on lapses and violations of the teachings of Jesus, the Prophets, the Law. Not over what Walter Brueggemann has called the "pelvic theology" that is obsessed with sex (though there are aspects of that which must be addressed when they result in unwanted pregnancy, injury, infection, injustice and denial of the personhood of someone), but over the central teachings of Jesus, etc. which informed all of the successful reform efforts in the history of the United States up to and including today's LGBT rights agitation. I don't see any prospect for anything but addressing those in terms of Christianity working. The "secular" really atheist, attempts to address those only seem to enable their fellow materialists of the most vulgar kind considered to be on the "right". I would include the Trumpian "Christians" among such people.
Given the importance that a decent, egalitarian, democratic United States is in the interest of everyone in the world, given the only way that is going to come about, I think it is in the interest of everyone who isn't some form of fascist, those call fascists or the red-fascism of Marxism, the billionaire oligarch class and others who favor the most vulgar of materialism or other assorted psychopaths and malignant sorts, that the kind of Christianity is revived in the United States. It certainly won't be easy but the atheists, oh, yeah, "secularists" have had their chance over the past fifty years and they have made a total botch of it. We don't have fifty more years to let them try to get it right. What worked to end slavery, give women the franchise, etc. has a proven record. They don't.
* Materialist anarchism is also properly identified with violence and terrorism and pointlessness, as seen in everything from the dogma of "propaganda of the deed" as advocated by Emma Goldman to the thrill seeking cult of thugs in Black Bloc anarchism which is doing its best to discredit the current left. "Leftists" of that type have such a habit of indulging a childish love of thrills and violence which is obviously more important to them than anything else. Such "anarchists" would immediately turn into Nazi style fascists in the absence of civil authority.
** As seen in Britain and some other countries, more or less rigid caste systems are able to arise even when people profess Christianity but refuse to follow the radical egalitarianism of the Law, the Prophets and the Gospel. No one who violates the basic principles of the religion they profess can, in any way, be considered as a refutation of the principles. No more than Donald Trump, George W. Bush or Ronald Reagan, Jeff Sessions, Jesse Helms, Rahm Emanuel could refute those truths which Jefferson listed in the Declaration of Independence or the principles that Abraham Lincoln asserted.