Given that we exist for no other reason than God desired it so and his motives for this are unknown to us , what can we derive about our nature and the nature of God? Let’s start back at the first inflection point in the development of what we call “human nature.” Although there is indubitably a great number of very profound truths in Genesis 1 and 2, I want to use the contrast in Genesis 3, the story of The Fall, to bring to relief certain other truths—perhaps less fundamental, but arguably more applicable to our present existence. After the Original Sin of eating the fruit from the Tree of the Knowledge of Good and Evil, God curses man and female-kind:
To the woman he said,
“I will surely multiply your pain in childbearing;
in pain you shall bring forth children.
Your desire shall be for your husband,
and he shall rule over you.”
And to Adam he said,
“Because you have listened to the voice of your wife
and have eaten of the tree
of which I commanded you,
‘You shall not eat of it,’
cursed is the ground because of you;
in pain you shall eat of it all the days of your life;
thorns and thistles it shall bring forth for you;
and you shall eat the plants of the field.
By the sweat of your face
you shall eat bread,
till you return to the ground,
for out of it you were taken;
for you are dust,
and to dust you shall return.” 
After which, Adam and Eve are cast out from the Garden of Eden.
Besides explaining (not to say condoning) however many millennia of chauvinism and general disenfranchisement of women, we can draw see several contrasts:
- Before Sin, Adam and Eve were of equal standing. Genesis 1 says “male and female he created them” with a clear delineation, but no other distinction. In Genesis 2, Adam calls Eve “flesh of my flesh and bone of my bone” showing equality to him. It is only after The Fall that men begin to ‘rule’ over women.
- After Sin, the Earth is no longer in harmony with humanity. It’s implied that Adam understands what thistles and weeds are, so the salient feature of this curse is not that a new plant is created, but that sin has opened up a significant rift between humanity and nature.
- Most significant, the beginning of Sin is the end of God’s walks with humanity. There are several notable exceptions to this throughout the Bible (Enoch, Abraham, Moses, Road to Emmaus, etc.), but it’s clear that a familiar—almost familial—bond was broken.
In other words, the direct result of sin is to change what was a harmonious symbiosis between humans and other humans, humans and nature, and humans and God into “dischord.” Whether this is a literal account of two individuals named Adam and Eve or if this is the precursor to Thomas Hobbes’ thought experiment on the “state of nature”  does not change this fundamental truth.
Let’s expand this line of thinking further. God creates humanity and puts us in perfect harmony with everything around us. He set up the parameters for how life is to work in this world, and absent the knowledge (a prerequisite of desire) for evil, everything ran in equilibrium according to these parameters. Once Sin is introduced, the natures of humanity, nature, and God have perhaps been tarnished, but have not been fundamentally changed. Rather, Sin disrupts the equilibria of the Garden and connects disparate elements of our natures; e.g. our domination of creation from Genesis 1:28 into our relationships with each other. And it creates enmity between elements of this previous orchestra that God had intended to play together: like man caring for and tending to creation, not just dominating it.
For a far more complete discussion on Sin, it’s effects, and the mechanisms by which Sin begets more Sin (including a discussion of why that one piece of fruit was the “original” Sin), I highly recommend Plantinga’s Not the Way it’s Supposed to be . “Sin corrupts: it puts asunder what God had joined together and joins together what God had put asunder.” 
In other words, Sin is the deviation from the parameters that are hard-wired into our (and the rest of creation’s) nature. When God lists out the “thou shalt’s and thou shalt not’s” of the Bible, He is, in some ways, creating a silhouetted outline or stencil of how we were created to be .
We may not be able to know beyond speculation what our purpose is , but again, viewing God’s commandments as a vector extending from some intention, we can at least get a Rutherford-like  view at some subset of God’s intended purpose. Because we were created at peace, in accord with God, and in accordance to the purpose for which he created us, and because sin causes us to deviate from that purpose, it is therefore to appease our nature to avoid sinning, as prescribed in the Bible . As long as we continue sin, we create greater cognitive dissonance within ourselves and larger rifts between ourselves, others, creation and God. It is only when we achieve perfection that we can (hypothetically) be free from the cognitive dissonance created by living in discord with one’s true nature.
Which actions or inactions are or are not Sins is not only well outside the scope of this article, but also a tedious and generally unproductive topic. More germane to the larger framework  is that God has defined rules for living that are consistent with his intended purpose for us; that is, the reason for which he created us. Sin necessarily joins us in ways that do not allow us to connect to— or tear us asunder from—God and leaves us incapable of fulfilling whatever purpose God had in mind when he created us. If we cannot meet that purpose, we cannot be called successful creations (like my box is not really a box if it cannot hold anything ), and therefore ought be discarded.
I have now laid out what I believe to be the essential framework for discussing any of the questions and multifaceted views laid out in the opening remarks . Nothing I’ve said was intended to be particularly profound, or even original, but I needed to establish a the parameters for the subsequent debates. Even if you don’t agree with the postulations I’ve laid out and don’t believe them to be axioms, I ask you to show Aristotle’s mark  and accept them for the sake of the subsequent arguments and discussion.
That tattooed Economist sends his love.
 Genesis 3:16-19; ESV
 Leviathan, Chapter 8, http://oregonstate.edu/instruct/phl302/texts/hobbes/leviathan-c.html
 Ibid, Page 30
 Similar to, albeit the opposite of, C.S. Lewis’ “Photographic Negative” used to describe his satirical work, The Screwtape Letters. http://www.amazon.com/The-Screwtape-Letters-C-Lewis/dp/0060652934
 1 John; Jude; Countless other books and passages throughout the old and new testaments.