An extraordinary aspect of what the Buddha discovered, so long ago — the knowledge of which has survived in theory and practice to this day — is that it is still not recognised in non-Buddhist cultures. It has not been absorbed into our ‘western’ knowledge-base, our way of understanding the world. (To what extent it is really present in eastern ways of thinking I cannot say.) Even now, when piecemeal chunks of Buddhist teaching or practice are chipped off and offered for their temporary and limited benefit, most people do not know what Buddhist wisdom could offer them.
What was the brilliance of what Buddha discovered for himself and taught others to find? He first expressed it to his fellow seekers in terms of four things which those on the path to this wisdom could investigate, find true for themselves, and integrate into the way they live. Although referred to as the Four Noble Truths, they are not simply a credo, statements to be believed and followed, that is not the Buddhist way at all. Everything is to be tested in personal experience, and there is a task associated with each of the four in order for it to have its effect.
the first revolutionary realisation
The world is riven with disputes, wars, life’s great sufferings, and a spectrum of unhappiness right down to a pervasive sense of restlessness and mental agitation. The Buddha’s first realisation was a diagnosis and an earth-shattering one: all these troubles, with their multifarious apparent causes, are actually the same ‘disease’.
If that is not a revolution in understanding, what is? He saw past all the conditions and explanations right to the root of our situation. The word he gave for the ‘disease’, one word to cover it all, was “dukkha“. In my view it is a great mistake to use our English word “suffering” to translate this — in fact it is a mistake to translate it into any language, because then we think we know what it is. If we know it already, we don’t look. And looking is essential to make use of this revelatory proclamation.
don’t call it “suffering”!
When the word ‘dukkha‘ is taken as meaning “suffering”, just anything unpleasant, it appears that Buddha is saying something plainly obvious: “association with the unbeloved is [suffering]; separation from the loved is [suffering]; not getting what is wanted is [suffering]… sorrow, lamentation, pain, grief, & despair are [suffering]”. Understood as naming a symptom in this way, ‘dukkha‘ becomes merely a broader vision of the unpleasant.
But taken as the name for a universal disease, the word equates the whole range of possible sufferings as being of the same nature. This I take as the reason why he had to explain, when he described his first “Noble Truth”, to which sufferings his term applied. (SN 56.11) 
Dukkha is actually much vaster in its compass than we could at first possibly imagine, certainly not as limited as our term “suffering”. Its spectrum runs from a pervasive sense of restlessness and constant need to interfere with our circumstances, through what we take as happiness or relief from suffering but is still temporary and dependent, finally to include birth, ageing and death. Yes, they are all symptoms of the same disease, he was making a bold claim! (SN56.11)
the point of meditation
The task for those who wish to follow this teaching is to fully comprehend dukkha: its diversity, its cause and its result should be fully known. (A.N. 6.63) So Buddhist practice begins with becoming interested in any instances of dukkha and coming to know them fully in our experience. What could possibly unite all these unwanted “heart-aches and the thousand natural shocks that flesh is heir to”? 
Looking at the particular circumstances of each one would be an endless task; looking at the subject who is suffering, specifically the mental origin of dukkha, would seem a better bet. Meditation, which had been used to attain states of tranquillity by contemporary teachers, now had a new investigative use.
the second breakthrough
The second truth of the “Aryas“, those on the unmistaken path to liberation from dukkha, spells out the uniting factor of all dukkha. It also makes another revolutionary claim, previously unrealised, without which there would be no point in naming the disease: dukkha has a cause. The reason all dukkha is one and the same is that there is one same cause for all of it. Buddha then tells that cause, or at least, where to look for it.
Here again, there is a task – it is not enough to have someone else name the cause for you, you need to see this cause for yourself – in yourself. Furthermore, since the cause is actively made, albeit unwittingly, you have to abandon that way of dealing with your experience. This entails examining that experience minutely to see how your mind works – and where the grain of sand in its machinery is disrupting its performance.
The correctness of the comprehension you obtain is verified by the result – liberation from dukkha. Is that very possibility not another “bombshell” of wisdom which has not permeated western consciousness, its philosophy, science, medicine, psychology, or social organisation?
breakthroughs are not enough
In this foundational teaching the Buddha is often compared to a doctor: he has diagnosed the diverse symptoms as being one disease, and he has found the single cause of that disease – a cause which is removable. It is not removable by anyone but yourself – that must be directly experienced in person.
But this is no simple matter, a lifetime of ‘existential sickness’ (in fact, uncountable lifetimes) cannot be cured at a stroke; no, a lifestyle change is called for, in line with this new understanding. It needs to permeate, to develop, to be lived out: this is how to put the remedy into practice. This prescription he spelled out in eight points, as the path of those who have fully comprehended dukkha, recognised its cause experientially, directly experienced abandoning it, and now wish to develop this path to full liberation.
 References to Pali suttas from http://www.accesstoinsight.org
 “Thousand natural shocks” quotation from Hamlet