Religion

"Usually the good Lord works in mysterious ways... Not today. This here is sixty-six tons of straight up, H-E-spewing divine intervention! If God is love, then you can call me Cupid!"

- Avery Johnson, boosting morale beside a recently delivered tank

A religion is a set of tenets and practices, often centered upon specific supernatural and moral claims about reality, the cosmos, and human nature, and often codified as prayer, ritual, or religious law. Religion also encompasses ancestral or cultural traditions, writings, history, and mythology, as well as personal faith and religious experience. The term "religion" refers to both the personal practices related to communal faith and to group rituals and communication stemming from shared conviction.

Buddhism
Buddhism is a religion and philosophy significant variation in beliefs among its adherents. Buddhism is based on the teachings of Gautama Buddha, sometimes known simply as "The Buddha", who lived during the fifth century B.C.E. in what is now Nepal and the Indian states of Uttar, Pradesh and Bihar located in the northeastern region of the Indian subcontinent. All traditions recognize Gautama Buddha as an enlightened teacher who shared his insights in order to help sentient beings end their suffering in accordance with the laws of Karma by understanding the Four Noble Truths; realizing the true nature of phenomena and thereby escaping the cycle of suffering and rebirth known to Buddhists as Saṃsāra. Among the methods Buddhist schools apply towards that goal are ethical conduct, the cultivation of wisdom, the training of one's mind through learning and meditation, altruistic behavior, renunciation of worldy matters, devotional practices and, in some branches, the invocation of holy beings to seek their help in achieving Nirvana. A Buddhist is one who takes refuge in The Three Jewels: Buddha; one who is Awakened, Dharma; The Teaching (of Buddha), and Sangha; The Community (of Buddhists).

Zen
Zen is a form of Buddhism that became popular in China and Japan and that lays special emphasis on meditation. According to Charles S. Prebish: "Although a variety of Zen 'schools' developed in Japan, they all emphasize Zen as a teaching that does not depend on sacred texts, that provides the potential for direct realization, that the realization attained is none other than the Buddha nature possessed by each sentient being ...". Zen places less emphasis on scriptures than some other forms of Buddhism and prefers to focus on direct spiritual breakthroughs to truth.

Smart AIs, having the short lifespan of seven years, often look to Zen. Koans, spiritual questions on which Buddhists meditate, are popular subjects of intrigue.

Christianity
Christianity is a monotheistic religion centered on the life and teachings of Jesus of Nazareth as presented in the New Testament. Its followers, known as Christians, believe that Jesus is the begotten Son of God and the Messiah (Christ) prophesied in the Old Testament. To Christians, Jesus Christ is a teacher, the model of a virtuous life, the revealer and son of God, and most importantly the savior of humanity who suffered, died, and was resurrected to bring about salvation from sin. Christians maintain that Jesus ascended into heaven, and most denominations teach that Jesus will return to judge the living and the dead, granting everlasting life to his followers.

Covenant Religion
The Covenant (later Covenant Loyalist) religion, given no specific name, is a polytheistic religion that centers around the belief that godhood is a state attainable by mortals and that the Forerunner attained such a state through activation of the Halo, which sent them on their Great Journey to salvation. Originating as the belief system of the San'Shyuum, it was eventually adopted and, to an extent, modified by the various races that would later join the Covenant, with the most devoted new members being the Sangheili and the Jiralhanae. It would continue even after the end of the Covenant as the Sangheili faith, although modified by recent revelations concerning the true purpose of the Halo Array.

Forerunner Religion
The Forerunner religion, its name unknown, was a polytheistic religion based on the belief in Precursors, god-like creatures with the power to travel intergalactically and accelerate the evolution of intelligent life. It is implied that the Forerunners believed the Precursors had given them the Mantle, a source of Forerunner authority.