The world's principal religions and spiritual traditions may be classified into a small number of major groups, though this is not a uniform practice. This theory began in the 18th century with the goal of recognizing the relative degrees of civility in different societies, but this concept of a ranking order has since fallen into disrepute in many contemporary cultures.
Unity of religion is a core teaching of the Baháʼí Faith which states that there is a fundamental unity in many of the world's religions. The principle states that the teachings of the major religions are part of a single plan directed from the same God. It is one of the core teachings of the Baháʼí Faith, alongside the unity of God, and the unity of humanity.
The Baháʼí teachings state that there is but one religion which is progressively revealed by God, through prophets/messengers, as humanity matures and its capacity to understand also grows. The outward differences in the religions, the Baháʼí writings state, are due to the exigencies of the time and place the religion was revealed.