This is the point of view pioneered by Harry Jaffa in a nutshell, a Jew who saw Lincoln as a restorer of the principles of the Declaration, which go back to Aristotle, starting from John Locke.
Not mentioned by the Christians here:
And yet Lincoln emphasized the Declaration of Independence far more than the Bible in building his case against human bondage. He described the assertion that “all men are created equal” as his “ancient faith.” He argued pointedly that the immorality of slavery could be proved “without reference to revelation.” In sum, without penetrating Lincoln’s heart, it’s hard to know whether he viewed the Bible as morally authoritative, as Leidner claims, or selectively cited it when it corroborated what he already believed.