The essence of Buddha’s teaching is summarized in the Four Seals:

First, all Compounded Things are Impermanent.
Second, All Contaiminated Things are Suffering.
Third, All Phenomena Are Empty and Selfless.
Fourth, Nirvana, Passing Beyond Sorrow, Is Peace.

Although Buddha first says very clearly, that all compounded things are impermanent, our minds cling to compounded things, ourselves in particular, as permanent and truly existent.

On that basis we make our first mistake.

Although Buddha clearly says that all contaminated things are suffering, we sentient beings cling to the contaminated happiness of our five senses as pure, perfect, happiness.

Thus comes our second mistake.

Then, although Buddha clearly says that all phenomena are empty and selfless, we sentient beings cling to all the external phenomena we perceive through our senses as inherently, truly existent.

Thus comes our third mistake.

Finally Buddha says that nirvana is peace.  He is speaking about a mind that is unmistaken in its way of seeing; not a mind that is mistaken.  Therefore this peace of nirvana is something that has receded very far from us.  This is because our mind has gone in a mistaken direction.

In any case, Buddha instructs us with a mother’s love. Although Buddha clearly guides us to an unmistaken perfect path, saying do this, on this path you will find happiness, and don’t do this, if you do, it will ring you suffering; still we sentient beings insist on going in mistaken directions.

Excerpt from  Precious Teachings, by Khenpo Karten Rinpoche, page 61 in print version (67 in PDF version), “Essence of Buddhism as Related to the Four Noble Truths.”