The term "religion" refers to both the personal practices related to communal faith and to group rituals and communication stemming from shared conviction. Religions is derived from the word region, it spring from cultures (to cultivate) which are different depending on values of individual or group.
Because the one "truth" is extremely difficult for any human to understand. So, we can only comprehend certain concepts at a time. Religions or faiths or philosophies concentrate on different aspects of what is one ultimate "truth."
Since we live in this vast world full of variety, there are many outlets that induce thought to the nature of our existence from what it is, to how it works, to how we fit in the picture, what are possible intentions of existence for as alive as we are. People, i.e. each individual, have different perceptions of reality. Even twins, raised in the same family, have different perceptions of the world. It's inherent in being an 'individual'.
However, there is a fundamental ideology according to which each individual seeks truth. This ideology is “everyone is in search of Eternity, Knowledge and Bliss”.