Dignity is an innate, inward state or condition emanating from a sense of personal worth. It is intuitively, immediately apprehended by human beings. It is neither learned, i.e, a social construct or convention, nor achieved, i.e., earned. It is distinguished from self-esteem, which is the conscious person speaking of himself, e.g, "I am a valuable person". Dignity flows in the opposite direction -- it results from the self speaking to the person, "you are a person, you have value". Being intrinsic, it cannot be completely destroyed, although sin and circumstances come close to doing so at times.
Empirical science can neither detect nor quantify dignity. I may recoginze this sense in myself, but I have no way of knowing that you do too. Like, e.g., the mind, it is a phenomenon directly accessible only to the individual self. But, because it is directly accessible to the individual person, we can talk about it without submitting it to the reductionist act of defining it. Just as we can talk about pain without defining pain. Or the mind. In the case of dignity, because of its sublimity, something is lost by attempting to reduce it to mere definition. It is a subtle sense painted on our inner psyche.
It is not to be equated or confused with outwardly dignified appearance, manner, deportment, or behavior -- although these may, of course, be associated with it.
I have been with persons who were in an outwardly undignified state. Persons in nursing homes for example, with all kinds aberrant mental behavior happening, and all kinds of bodily fluids and other expulsions being expresed in unseemly ways. Where is the dignity in this? There is seemingly none.
Or the Nazi concentration camps. Nude skeletal prisoners, and dead nude prisoners stacked like cordwood. Where's the dignity in this?
At this point, faith (or atheism) kicks in. If atheism, you will go along with Hitchens and view the dead Jews' bodies as "carcasses". Alternatively, you might view Dawkins more to your liking, where the sum total of what it means to be human can be summed up in the observation that organisms, humans among them are “throwaway survival machines”. Carcass or throwaway survival machine -- take your pick -- because it is impossible, under atheism that they could be anything more -- unless you are content to base the human sense of dignity on nothing more substantial than an ungrounded irrational sentiment.
More likely, faith (or something akin to faith) kicks in. We look beyond the mere outward appearance and ascribe dignity to the person, no matter how battered the human being may be by age, infirmity, sin, or circumstances. Why? We ascribe dignity to the person precisely because they are a person. We extend dignity to the human body precisely because it was the body of a person, and not an animal.
Dignity is an intrinsic quality of personhood, experienced (I think), as what philosophers refer to as a quale. The only sufficient cause of real, authentic dignity is man created in God's image.
To the darwinian, this inward sense of dignity can be nothing more than a chimera, an illusion, a falsehood of biochemical evolution. When the self whispers to us our value, and a sense of dignity ensues, it cannot be authentic because it cannot be not grounded in anything beyond dumb, mindless, (and in this case ultimately cruel) biochemical operations.
To the theist, it is an indicator, however faint, of our ultimate origins in God.
Faith -- the evidence of things not seen, the assurance of things hoped for.
Rejoice that you are human.
And that's the way the Ball bounces.