In the third part of I and Thou Buber finally brings God into the picture. He has already told us that the solution to man's psychological and social ills is going to involve building a new sort of community, one built on encounter. Now he tells us more specifically how we are to go about putting this solution to work. What we need to do, first of all, is move from encountering human beings and nature, to encountering the eternal You, God.
The need to encounter God, Buber tells us, is evident through all of our human encounters. As each human encounter inevitably peters out into experience, we sense, in our disappointment, that there is something more that we want. In this way, we come to realize that we are longing for absolute encounter: that is, for encounter with God, the eternal You that can never degenerate into an It. Once we realize that we want an encounter with God, we must simply ready ourselves for it and it will take place.
Readying ourselves for encounter with God is one of those mysterious processes that Buber claims is indescribable. However, he does indicate three necessary ingredients in the process. First and foremost, in order to encounter God we must truly want to encounter God. Second, in order to truly want to encounter God we must get rid of the drive toward self-affirmation (i.e. the drive toward justifying our actions and the drive toward seeing ourselves as in control) because this drive leaves us clinging desperately to the predictable and understandable mode of experience. Finally, we must hold together all of the irreconcilable parts of our self (such as the I of I–It and the I of I–Thou) in a state of paradoxical harmony, a concentration of the soul. Once we are ready for absolute encounter, we can only wait for God to meet us. And he inevitably will. No matter what one's conception of God—if one thinks of God as Buddha, as Christ, or as the God of Israel—if one addresses God with their whole being, and are ready for absolute encounter, they will encounter God.
Buber calls the moment of readiness for divine encounter, "man's decisive moment". Encounter, he tells us, is both active and passive. It is supremely active, on the one hand, because we must will it to occur with our whole being. On the other hand, it is passive because it is not enough to prepare ourselves to meet God, we must also be met. Absolute encounter (encounter with God) involves both choosing and being chosen.
In absolute encounter, God fills the universe for us in a similar way that the other person does in interpersonal encounter. But the way that God fills the universe is different: when we enter into relationship to God we are also entering into relationship with everything else in the world, because encountering God involves encountering everything belonging to God, that is, the world. In absolute relation, we do not ignore the rest of the world, but relate to it through relating to God. We comprehend the world while comprehending God, though not in the sense that we believe (falsely) that the world just is God, or God just the world. Instead, we simply understand the universe as it stands in relation to God. Because of this, the absolute encounter is both exclusive and inclusive. It is exclusive, much like other encounter, because we relate to the You as if it were all that mattered for us, and see the rest of the universe through its light. It is inclusive because it is not just the divine being but also His entire universe with whom we are relating in this way.
Buber thinks that we reach God through encounter with human beings or with nature. In every fleeting You we get a glimpse of the eternal You and sense the possibility of absolute encounter. We know that there is the possibility of absolute encounter, in other words, in the same way that we know there is the possibility of encounter at all: because we sense that it is the only means for fulfilling a basic human need. Once again, the same objection can be posed, namely, assuming we even have this need, why believe that it can be satisfied? Again, Buber does not seem to be making an argument for the existence of absolute encounter, but merely describing how it is that we happen to become aware of the possibility of absolute encounter. Again, this leaves Buber with no argument at all for one of his central claims, but there is the possibility that this is how he wanted it. Perhaps the proof for the existence of divine encounter is supposed to lie in our active attempts to reach this encounter. If we reach it, we have proof that it exists. If not, we have no such proof. Since Buber's goal is not simply to intellectually convince that he is speaking truth, but to actually make us put his words into action, this sort of proof might suit his purposes well.