The doctrine of the last day and eschatology (the final fate of the universe) may be reckoned as the second great doctrine of the Quran. It is estimated that approximately one-third of the Quran is eschatological, dealing with the afterlife in the next world and with the day of judgment at the end of time. There is a reference to the afterlife on most pages of the Quran and belief in the afterlife is often referred to in conjunction with belief in God as in the common expression: "Believe in God and the last day."