The Hebrew verb Shaba, to swear, is evidently derived from Sheba seven, and denoted a sevenfold affirmation. Herodotus (xiii. 8), tells us the manner of swearing among the ancient Arabians included smearing seven stones with blood. Sheba is allied to the Egyptian Seb-ti (5-2), the Zend Hapta, Greek Epta, Latin septem. The Pythagoreans said that Heptad came from the Greek Sebo to venerate, but Egyptian and other African dialects suffice to prove it is far earlier.
The writer of the Apocalypse had the mystic number on the brain. Dr. Milligan has explained the 666 number of the beast, as a fall below the sacred seven John of Patmos gives us seven golden candlesticks, (i. 1), seven stars (i. 20), seven spirits and churches (iii. 1), seven seals (v. 1), trumpets (viii. 2), thunders (x. 34), vials (xvi. 1), and seven angels with seven plagues (xvi.) The beast has seven heads, horns and crowns (xii. 3, xiii. 1, xvii. 7). The Lamb with seven horns and seven eyes (v. 1 ). There are seven spirits before the throne of God (Rev. i. 4, etc.) like the seven Dhyani Chohans emanating from Parabrahm in Hindu Theosophy.
So Christians have kept up legends of seven wise men, seven wonders of the world, seven champions of Christendom, seven cardinal virtues, seven deadly sins, seven devils in Mary Magdalene, etc. Of course there is no better reason why there should be seven than the old idea of mystery and completion attached to the number.
Modern Theosophists, too, go in largely for the number seven. There are seven planets, seven rounds on each planet and seven races. Every ego is composed of seven principles—Atma, Buddhi, Manas, Kamarupa, Linga Sharira, Prana, and Sthula Sharira. It may seem strange that a lady of Madame Blavatsky's undoubted powers of imagination should run in the old rut. But the well-worn superstitions work the easiest, although to every instructed person this one carries the mind back to the days when men knew only of seven planets and measured their time by the moon.