Your equation of Divine Truths which were not written down in the Bible with "humanism" merely marks you as a Protestant. If everything not written down is "humanism," then you'd better toss all the vowels and punctuation marks out of your "old testament," because these were not written down but preserved orally.
I'd also be interested in hearing how you think the ancient Israelites intercalated their calendar with nothing written down in the Bible about it. Was it "humanism" to see to it that Passover always came in the spring by adding an extra month every few years?
Technically, David was neither a murderer nor an adulterer, because the conditional divorces which were given to soldiers before going to battle were retroactive up to the time they left. Yes, what David did was beneath him which is why it is held against him in Scripture, but—admittedly by a technicality—he was neither of these things.
So why did God send Nathan to David with the story of the poor man, the rich man, and the sheep?
Why did God (via Nathan the prophet) tell David “Why did you despise the word of the LORD by doing what is evil in his eyes?”
Why did God punish David (”Out of your own household I am going to bring calamity on you.”) for these actions?
Why did David respond to all this by saying “I have sinned against the LORD.”?
You are confusing ethnocentrism and society with humanism.
Humanism –noun
1. any system or mode of thought or action in which human interests, values, and dignity predominate.
2. devotion to or study of the humanities.
3. ( sometimes initial capital letter ) the studies, principles, or culture of the humanists.
4. Philosophy. a variety of ethical theory and practice that emphasizes reason, scientific inquiry, and human fulfillment in the natural world and often rejects the importance of belief in god.
Ethnocentrism –noun
1. Sociology. the belief in the inherent superiority of one’s own ethnic group or culture.
2. **a tendency to view alien groups or cultures from the perspective of one’s own.**
Society –noun
1. an organized group of persons associated together for religious, benevolent, cultural, scientific, political, patriotic, or other purposes.
2. a body of individuals living as members of a community; community.
3. the body of human beings generally, associated or viewed as members of a community: the evolution of human society.
4. a highly structured system of human organization for large-scale community living that normally furnishes protection, continuity, security, and a national identity for its members: American society.
[...]
Much of the Bible is humanistic, in the sense of definition #1; the Law, for example, is predominately about how Man should behave in a manner that shows values and dignity in self and in other [men]... even the Capital Punishment Directive of the Noah-Covenant (Gen 9:5-6 — “And surely for your lifeblood I will require an accounting; from every beast I will require it; and from man, from every man [who spills another’s lifeblood] I will require a reckoning. Whoever sheds man’s blood, by man shall his blood be shed; for in the image of God He made man.”)
There is nothing ‘humanistic’ (any def) about “the vowels and punctuation” of the old testament; it is the art of translation to take the meaning of something in some language and express the same in another, transliteration is [word-for-word substitution] results in something closer to the “what was said.” Idioms are a good example; the phrase “between a rock and a hard place” transliterated into Spanish would have little of the original meaning carried by the saying, but they have a saying that carries the same concept [transliterated to English] it is “between the sword and the wall.” (Yes it *is* understandable in transliterated form; but the goal of communication is not to be possibly understood, but to be impossibly misunderstood.)
Regarding your claim that David didn’t commit adultury, technically; then explain this, Jesus said: “I tell you that anyone who divorces his wife, except for marital unfaithfulness, and marries another woman commits adultery.” [Mat 19:9]
Are you going to tell me that Jesus has no authority to speak on the matter?
Are you going to tell me that following tradition *IS* acting righteously? Didn’t Jesus also condemn the religious leaders of his day for their traditions? If so, then explain Jesus’s summation of “Thus you nullify the word of God by your tradition that you have handed down. And you do many things like that.” [Matt 3:17; in response to allowing someone to basically put into a trust “for the Lord” things that could otherwise be used to help their parents in need. Much akin to *showing* that the parents are worthless by pushing them off into ‘homes’ that American society does today.]