Seven is heavily loaded in religious thought, and it is worth noting that its weight came from the sky rather than from geometry.
The classical world counted seven moving bodies against the fixed stars: Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn. That count fixed the seven-day week, the naming of the days, the seven metals of alchemy, and much of the planetary correspondence that later esoteric systems inherited. Babylonian astronomy is the source, and the transmission through Greek and Roman practice into the calendar is well documented.
In the Hebrew Bible seven governs the structure of the creation account, the seventh-day sabbath, the sabbatical year, the jubilee after seven sevens, and the seven-branched menorah of the Temple. Revelation is built on sevens throughout: churches, seals, trumpets and bowls. In Islam there are seven heavens, seven circuits of the Kaaba, and seven verses in the opening sura.
Indian tradition counts seven chakras in the systems now most widely known in the West, though that is not the only enumeration in the source texts, several of which give four, five, six or a different number, and the standard modern seven-chakra scheme owes a good deal to how the material was received and simplified in the twentieth century. Seven Hathors appear in Egyptian texts as determiners of fate, and the seven sages, the saptarishi, name the stars of the Plough in Indian astronomy.
The heptagram or seven-pointed star is used in several modern traditions, as an emblem in Thelema, in some Wiccan practice, and in modern devotional design. It has no significant premodern architectural presence, for the straightforward reason that nobody could draw one exactly.