Among the definitions given here, definition number four looks to be the basic definition from which sprung all the others.
4. A cause, principle, or activity pursued with zeal or conscientious devotion.Beliefs about supernatural powers would then represent one, common way that people can be inspired to zealous devotion. Why this zeal? What's the purpose?
Middle English religioun, from Old French religion, from Latin religi, religin-, perhaps from religre, to tie fast."Religion" likely evolved from the Latin verb "religare", "to tie fast", or "to tightly connect", or "to bind again".
Latin religre, to bind fast : re-, re- + ligre, to bindFrom "religare" comes the English word "rely". From "ligare" comes words like "ligate", "oblige", and "league".
"Re-" prefix carries a particular meaning, "again" or "back". To bind again implies that a prior binding, or union, existed.
To practice religion is to re-connect with what you had lost. The need to practice religion implies that one is not fully whole, that there is something missing. In Eastern Orthodox Christian terms, what was lost was the intimate communion with God in the Garden of Eden; and Jesus Christ becomes the way by which the communion is not simply restored but also cultivated and perfected. In Meher Baba's theo-cosmology, what was lost was unity with God; and Meher Baba becomes the way by which that unity is not simply restored but also cultivated and perfected. I'm not too sure about the Orthodox position on this issue, but for Meher Baba, the priori unity of God was an unconscious unity. God wanted to become conscious, and thus asked "Who am I?", simultaneously leading to the creation of the cosmos and of living beings within, and a part of, that cosmos. Living beings then evolve their separate centers of awareness, from atoms on up to mankind. Mankind is then able to evolve in spiritual awareness, into re-union with God, but now this new God-Union (unlike the prior unconscious unity) is filled with awareness.
Religion can be seen as the process of making whole, of re-uniting separate parts.
Something that has healed is now whole. Both "whole" and "heal"; as well as "holy" and "hallow", as in "Hallowed be Thy name"; come from the same Indo-European root "kailo", "whole", "uninjured".
Religion then, essentially, is truly "holy": healing, health, and wholeness, whether physically, energetically, emotionally, intellectually, or spiritually.