Martin Esslin quotes
The Theatre of the Absurd has renounced arguing about the absurdity of the human condition; it merely presents it in being - that is, in terms of concrete stage images. This is the difference between the approach of the philosopher and that of the poet; the difference, to take an example from another sphere, between the idea of God in the works of Thomas Aquinas or Spinoza and the intuition of God in those of St. John of the Cross or Meister Eckhart - the difference between theory and experience.
Martin Esslin
The Theatre of the Absurd ... can be seen as the reflection of what seems to be the attitude most genuinely representative of our own time.  The hallmark of this attitude is its sense that the certitudes and unshakable basic assumptions of former ages have been swept away, that they have been tested and found wanting, that they have been discredited as cheap and somewhat childish illusions. The decline of religious faith was masked until the end of the Second World War by the substitute religions of faith in progress, nationalism, and various totalitarian fallacies. All this was shattered by the war.
Martin Esslin