The use of absurdity in Kafka's work expresses his inconformity with the absurdity of society. He explored the transformation of the individual by using an allegory--the transformation into an inscet--that also expressed a person's worthiness to society. The absurdity of the situation also relates to Kafka's existentialist ideas. In existentialism, there is no "meaning" behind anything. Existence is, in itself, absurd.
Existentialism refers to the philosophy dealing with the man's alonness in the universe--the idea that only the individual is responsible for himself. That either there is no God, or God has nothing to do with people's lives. At the same time, the fact that there is nothing beyond ourselves and our decisions means that there is no meaning; people need each other to give their lives meaning. In Metamorphosis, Kafka illustrates that by showing that the character cannot live in isolation and eventually dies. Being alone somehow "dehumanized" him.
Another existential idea relates to the unfairness of the meaninglessness of life. That we do not really have control, and things happen by chance. There is no order. Kafka also expresses that in this short story by showing the complete lack of control the character had over his metamorphosis. He could not help it as much as he could not prevent his death.