Nice - I agree with your last paragraph - how can Romans 2:14 refer to the Mosaic Law, since pagans did not have it? Clearly, the Law Paul is talking about there is what you and I call "Natural Law". An eternal and objective law of God based upon what is pleasing to Him on a more generic scale accessible to all men via their conscience.
Regards
To me the law written on the hearts of those who don't possess the literal written law is the
requirements of the law that all men know through conscience and nature.
But, I'm pretty sure Romans 2:14 is indirectly (but *profoundly* ) talking about the law of Moses when he makes the remark. For the law of Moses is a product of legal argumentation coming from Genesis and the Fathers (with a few concessions).
But, let's consider a test case: a dog has a law inscribed in it (brute beast law) that is "natural". And a dog, being the animal it is, sometimes considers a human leg to be a sexual target. Which is "natural" in the sense of that's what some breeds do instinctively... (and very annoyingly.)
It is not obvious, then, that all "non-hetersexual or homospecies(al)" disorders (and even it's definition as a disorder) is attack-able on the grounds of it being found in "nature"?
There are people who can learn depraved tendencies, of their free choice, or who were exposed to sexual violence at an early age; so it isn't as simple as all Nature or Nurture (to use the psychological terms.) But, assuredly, some people have no control over the feelings (but they do over the acts.) It's an illness in addition to a perversion in some cases.
So, when Paul talks about them "doing by nature"; I don't think he means what is inscribed in man's body by "nature"; or raw emotion; and conscience is rationalized by pain/urge relief. (Well, this is the way God MADE me, so it's natural and not wrong. -- some sufferers will claim.)
But, God says of the promise "I
WILL inscribe my law into their hearts.", (Hebrews 8:10 ἐπιγράψω future) by which we discover that they aren't there (completely) now; or else he need not do the work of inscribing them. ( John 6:29 This is the work of God, that you believe. )
Hence, I think God was always involved in inscribing them; one man at a time.
Some men will naturally do things, others naturally do the opposite; it's biological wiring.
There are even some men who have no sexual drive whatsoever; Matthew 19:12
( Ahh, that'd be nice for many men -- to see the ladies as true art, with no interference from biology. )
But notice carefully what Paul says in Romans 2:15.
"and their
thoughts the meanwhile accusing or
excusing one another."
Thoughts, is logismoi (logic). It is therefore, not memory or rhymes, or feelings [alone] but arguments which accuse or excuse.
A man can reason that the purpose of a woman having a womb, is to bear children; and the butt end of all of us -- is for excrement and sitting.
So, from these, we can *reason* to a law about their usage. Romans 1:26-28.
It is in this sense, a theology or law of the Body, which Genesis ( which means being/begetting ) is a law; it's a pre-done example for arguing what is "natural" and what isn't.
As I said, the Babylonians and other nations have records of the same stories found in Genesis; there are imperfect, twisted, but none the less -- they can
argue the case of what is the purpose of the body?
Without reason, though, there is no law; for there is no judgment, nor excuse or accusation.
Therefore, law is not a purely internal object; it's one that is grasped by human intellect and achieves it's strongest expression in society -- and Christians are not exempt.
Matthew 18:20, notice, makes the point nicely with respect to Christians.
It takes two or three witnesses to establish a case; one alone can't be a judge.
Now read Matthew 18:21-31 -- The parable is about judgment.
So we see natural law in action -- for the wicked servant did nothing technically against a written "law" (to the contrary, it was legal). But he was judged by another law that the servant
S internalized and witnessed to -- from an example of their "master".
Consider, then, exactly how Paul preached/taught on a "nature" basis:
Romans 1:19, Acts 17:27-29, Romans 1:25-28
Now, each nation has it's "Gods"; therefore, what is "nature" and what is "conscience" and what are "requirements" ?
I think some of this is semantics, but I bring it up as target practice. ;)
In Romans 2:14 -- Paul says "when they do by nature the things
contained in the Law."
The definite article in Paul's writing generally refers to the Law of Moses, and often to the prophets/psalms.