The seven of religious usage is remarkably consistent in function: it marks a complete set, and completeness is usually the point rather than the count.
Christianity. Revelation is built on sevens, seven churches, seals, trumpets and bowls. The seven sacraments were not fixed until the medieval West settled them, confirmed at the Second Council of Lyon in 1274 and definitively at Trent. The seven deadly sins descend from the eight evil thoughts of Evagrius Ponticus in the fourth century, reduced and reordered by Gregory the Great around 590; the familiar list is therefore an editorial product with a traceable history rather than a scriptural one. The seven gifts of the Spirit come from Isaiah 11:2, where the Hebrew gives six and the Greek Septuagint seven.
Islam. The Quran speaks of seven heavens at 2:29 and 65:12. The tawaf of the hajj is seven circuits of the Kaaba, and the sa'i is seven passages between Safa and Marwa; the stoning at Mina uses seven pebbles.
Judaism. Shiva, the seven days of mourning, takes its name from the number. The menorah has seven lamps. Shavuot follows seven weeks.
Zoroastrianism gives the seven Amesha Spentas, the beneficent immortals.
Indian tradition gives the seven rishis, identified with the stars of the Great Bear, and the seven chakras, a system that is genuinely attested in tantric texts, though the count varies between schools and the familiar rainbow colouring of them is a twentieth-century Western addition, traceable to Charles Leadbeater's The Chakras of 1927.
Japan gives the seven lucky gods, a group assembled in the Muromachi period from Shinto, Buddhist and Chinese sources, a late compilation, and a good illustration of how sevens get built.