This play is full of so many possible themes - you could have a complete field day in answering this question as an essay. But one overarching question seems to link all of these possible themes together - what is the nature of our existence as human beings?
We enter the world with no sense of identity and gradually as we grow up assume our identity from things around us - our families, our achievements etc. However, one of the major aspects of the play seems to point out that our assumed identity maybe based on illusory concepts. Beckett himself rejected the church as an "illusion" and believed that man's greatest achievements, when considered in the context of the whole universe, count for nothing, but at the same time, life without illusions of grandeur and importance would be a very sad affair.
In relation to this, you need to ask yourself what kind of world it is that Vladimir and Estragon live in. They don't have the normal securities that we do in our lives - nothing is certain, violence can appear be inflicted upon them at any time, and there are no concepts such as justice or securities of any afterlife. Even simple tasks are made out to be major achievements. The human condition is therefore depicted to be incredibly insecure, but perhaps the one redeeming feature is our search for meaning and significance.
Against this relentless nihilism of the play, another redeeming aspect is the friendship of Vladimir and Estragon, and it is worth the pain to examine their relationship based in the context of the whole play. What does their friendship say about hope in an otherwise hopeless environment? What hope does it offer to us as human beings as we struggle to make sense of who we are?
Thematically speaking, Godot has it all---from the ordinary to the sublime, from the suffering of putting on a misfit boot to the suffering caused by a divine absence. From a religious point of view, the play is about a quest for the transcendental order, frustrated by a radical lack of its presence, whereby the salvation-damnation (the TWO THIEVES section--allusion to Augustine) and sin-redemption binaries become very important. The idea of existence and an authentication of existence through the gaze of the Other is another major thematic issue at work. Remember what Vladimir tells the boys in both the acts, that he must tell Godot that he saw the two of them. Waiting, which is the basic condition of the couple on the stage is yet another theme in the play. Through Lucky and Pozzo, the themes of mastery and servitude and the ever shifty power dynamic is introduced into the play. A latent homosocial if not homoerotic bond between the Beckettian pseudo-couple Didi and Gogo, The Great Fall of Man (Lucky and Pozzo's fall in Act II), Crucifixion (they fall creating the form of the cross posturally),the speech-silence dichotomy, suicide and the serio-comical parody of its existentialist figuration, endless cyclicity of time and space, the impossibility of closure, a fight between nothingness and discursive non-sense, lack of the event are the other thematic issues at work in the play.
Waiting for Godot is about the meaninglessness of life. Vladimir and Estragon must find meaning on their search for it throughout the play and in life but are faced with the unspoken obstacle of being physically bound to the stage- they are never permitted to leave, which can be related to the trap of life.
It is also about questioning beliefs such as religion (has several biblical allusions) and has a post-world war context.
this play has only one significant theme and that is 'Nothing'
so this nothing is a keyword of the play which swallows all the rest of the possible themes i.e.death of culture,loss of identity,moral decadance,religious ambiguities, ethical deteriaration,intellectual inertia,atrocities of world war,postwar effect on humanity,exploitation of capitalism,dependance on some foriegn agency,alienation and so on.we cant restricted its canvass......and that is nothingness
waiting for godot is a play that has a theme in each and every dialogue still major themes are; the absurdity of life, human sufferings, free will, uncertainity vs. certainity and many more
emptiness of human life..... it's mean waiting for nothing