Morality cannot be demonstrated to exist or not exist [1], and certainly not by personal feelings or appeals to human governments or norms, but a person can, without they themself or their audience making assumptions, realize and share accurately what Mosaic Law is, what the logical prerequisites or ramifications to its various laws would be, and what evidence there is for Christianity, and thus for Biblical ethics being true. The existence of morality itself is entirely speculative either way, but at least Christian ethics is logically possible (it does not contradict logical axioms or other necessary truths) and has actual evidence in its favor; all other moral systems have none at all or contradict themselves or something else about reality that is true by logical necessity (for example, see just one of my many refutations of Islam here [2]). See these excerpts from Deuteronomy and Isaiah specifying that children do not know morality and have to in some way learn it (again, no person can actually know the existence or particulars of moral obligation, if it does exist, but one can teach to them the tenets of Judeo-Christianity and the evidences for them, and so on, or they can recognize them without social prompting):
Deuteronomy 1:39—"'And the little ones that you said would be taken captive, your children who do not yet know good from bad—they will enter the land. I will give it to them and they will take possession of it.'"
Isaiah 7:14-16—"'Therefore the Lord himself will give you a sign: The virgin will conceive and give birth to a son, and will call him Immanuel. He will be eating curds and honey when he knows enough to reject the wrong and choose the right, for before the boy knows enough to reject the wrong and choose the right, the land of the two kings you dread will be laid waste.'"
I used the New International Version above, which still conveys that in both cases, children do not know moral right and wrong left to themselves, though this is even more explicit in translations like the King James Version and the English Standard Version. According to very direct Biblical statements, no one knows morality by default. No one would have to learn or teach God's revealed laws from or to other people (Deuteronomy 6:6-7) if everyone just "knows" from subjective feelings what is right or wrong, which is already a logically impossible thing. God would have never had a reason to reveal any commands at all if this was the case. Emotions only require and prove that one's own emotions presently exist. Feelings have nothing to do either metaphysically or epistemologically with whether morality exists or what obligations there are. Since reason is inherently true, and thus the Bible would have to be consistent with logical necessities in order for its philosophy to even possibly be true, it is no small thing that the Bible does plainly deny innate moral knowledge. In fact, many people who claim to be Christians and profess moral knowledge through conscience would actively disregard or oppose Biblical commands while thinking that unrelated or innocent things are moral evils.
Conscience would not be any less subjective even if everyone's was the same, but would your conscience suggest that you always pay your laborers (employees or hired workers) before the next sunset (Leviticus 19:13, Deuteronomy 24:14-15)? Have you, if you have a conscience, ever been stricken left totally to yourself because you ate pork (Leviticus 11:1-3, 7-8, Deuteronomy 14:8) or thoughtlessly vowed to do even something good (Leviticus 5:4-5), not that you can know what is good beyond what is good if a given worldview is true? Such a feeling would still only require that you are experiencing guilt or moral concern, not that the thing itself is immoral, and you could never know objective morality from subjective conscience anyway. What about your feelings about the mandatory stoning of a family member to death for enticing you to worship anything besides Yahweh (Deuteronomy 13:6-10) or about the release of male and female slaves, which are Biblically permitted but so very different from the slaves of many other times and places, every seventh year and their furnishing with resources upon the end of their service (Deuteronomy 15:12-14)?
I doubt that anyone I have known would have ever had their conscience make it seem as if these and other such exact things are respectively obligatory, permissible, or evil. Even if someone's conscience did make them feel like these are the moral obligations that exist, the Bible concurs with what is logically true either way: no one "just knows" morality from conscience, which is purely subjective, not that everyone has a conscience to begin with, and not that everyone who has a conscience will not lose it or see it change. You cannot be taught by God or fellow humans what you already know, just as you cannot be given eternal life if you already have it and thus the unrighteous will not live, and hence cannot be tortured, forever (John 3:16, Romans 2:7-8, and so on). Perhaps a misinterpretation of Paul's writings in Romans 1-2 is what many Christians I have encountered base their philosophical notion to the contrary on, at least as far as what they think the Bible teaches on the subject of moral epistemology. Was this actually what Paul means, then his writings would contradict both the inherent truths of reason and the Old Testament doctrines he supposedly champions. The New Testament or certain parts of it can be false if the Old Testament is true, but not the other way around.
It is not as if the belief that conscience is an genuine confirmation of objective morality is limited to only evangelical Christians, however; it is quite a popular belief, or at least many talk and act as if they believe it, whatever the rest of their worldview is like, though this idea and all that it entails could by logical necessity only be false. People who have literally never paused to even examine the mountain of sheer assumptions on which their passively constructed worldview stands might have a thriving yet intrinsically arbitrary, irrelevant, and meaningless conscience; atheists, Muslims, and any other category of philosophical adherent could have a passionate conscience. Not even believing in moral nihilism, which cannot be proven or as much as evidentially supported even if it is true, necessitates that someone is without a conscience, and neither does lacking a conscience mean someone is not a fierce moralist of one kind or another. Not once does the Bible, its moral doctrines most precisely and almost exclusively introduced in the Torah's Law of Moses, say anything that denies any of this.
[1]. See here for a handful of my posts on this matter:
[2]. For instance, see here:






















