The symbolism of thirteen comes into play when we learn of Osiris (the Egyptian god of life, death and powerful solar symbol) was murdered by his brother Typhon. Isis, Osiris' wife and sister collected his body with intent to restore Osiris back to life.
However, Typhon stole Osiris' body and cut it into fourteen pieces and scattered them about the earth. Isis continued her quest to revive her beloved, but could only reclaim thirteen of the fourteen body parts (the fourteenth part being Osiris' penis which interestingly fell into the Nile and was eaten by a school of fish which are also symbolic).
This tale symbolically implies that the meaning of number thirteen is the precursor to completion.
Also in Egypt, there are thirteen steps upon the ladder that leads to eternity. Upon the thirteenth step it is said the soul reaches the source of itself and attains spiritual completion.
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