Why Should We Have Believe In Afterlife?
It is very much discussed in Quran. Without the Day of Judgement, the whole scheme of creation is meaningless. Good and bad will not meet their justified end. It is against the wisdom (Hikmat) of God. This message from God sent with Adam and kept coming to the humanity through out the history of prophets. You are referred to read the relevant verses in Quran espeically the last surahs of the Qruan starting from Surah Qaaf. We believe in it because we received this message from God though prophets.