The number 21 has symbolic meaning in many traditions, with special significance in the Jewish and Christian Scriptures. According to The Bible Study Site, it symbolizes willful wickedness. It is closely related to the number 13, which symbolizes sin, rebellion and depravity. Adding eight, which symbolizes fullness and eternity, to 13 yields 21, representing total wickedness or an increased level of sin.
Biblical numerologists explain that during their 40 years of exile in the desert, the ancient Israelites staged 21 notable rebellions against God and His priests. In his Second Letter to Timothy, Saint Paul lists 21 sinful behaviors of wicked people. The final behavior, described in the third chapter, is inward denial of God's power.
An alternate analysis of 21 as used in the Bible ascribes positive qualities to the number. It is the product of three, representing the fullness of the Holy Trinity, and seven, the number of days described in the creation account in the Book of Genesis. From this perspective, 21 represents the blessed unity of the Trinity with all creation.
New Age numerologists and astrologists ascribe various meanings to the number 21. According to numerologist Hans Decoz, individuals born on the 21st day of a month have great creative energy and feel motivated to work hard to achieve their goals. Decoz writes that such people are social magnets who inspire those around them with positive energy and optimism.