Ever wonder where the idea of the number seven as lucky came from? More likely than not, the idea of good luck associated with seven comes from the number 7 in the Bible.
Both Christian and Jewish traditions have used numbers to interpret the Bible, although the practice is more common to Judaism. The interpretation of scriptures by using numbers is known as "gematria," a Greek word meaning "calculations." Many cultural traditions of interpretation or good luck, such as the number 7 in the Bible, come from the practice of gematria.
The following glossary of some examples of the meaning of the number 7 in the Bible and other numbers is from The Encyclopedia of Jewish Mysticism, Myth and Magic by Rabbi Geoffrey Dennis.
1 The number one means divine unity, as shown by God.
3 Three means completeness and stability, as shown in several examples such as the Three Patriarchs recognized by Judaism: Abraham, Isaac and Jacob.
4 The number four recurs in many Jewish practices based on historical traditions, such as the Passover Seder, which is built around fours: Four Questions, Four Sons and four cups of wine.
5 Five is the number of protection, as symbolized by the chamsa, a talisman or charm in the shape of a hand.
7 The number 7 in the Bible is considered one of the most powerful and lucky numbers in scripture, according to the practice of gematria. A prime example is the Creation of the world, accomplished by God in seven days according to Genesis. The Hebrew word for "luck," gad, equals seven in gematria.
8 Eight represents completion, such as the eight-day festival of Chanukah.
10 Ten is considered another major symbol of power and good fortune, based on the Ten Commandments.
12 Twelve is thought to symbolize wholeness and the completion of God's purpose. There are 12 tribes of Israel, descended from the 12 sons of Jacob, as well as 12 months in a year.
24 The number 24 represents abundance in gematria. Its meaning is linked to the height of Jerusalem as a city, when it had 24 main roads, 24 side-streets, and 24 alleys leading to 24 houses.
40 The number 40 represents a time of radical transformation, such as the 40 days of the Great Flood in Genesis 7.
70 The number 70 symbolizes the world as represented by the 70 nations, each with its own princely angel, in Jewish mystical imagination.
Lastly, in gematria, odd numbers such as the number 7 in the Bible are considered lucky, while even numbers, particularly pairs, are thought to bring misfortune.
Source for the Meaning of Numbers in the Bible
Dennis, Rabbi Geoffrey W., The Encyclopedia of Jewish Myth, Magic and Mysticism (Minnesota, Llewllyn Publications, 2007), and his blog site, http://ejmmm2007.blogspot.com/