27 is 3 times 9, both of which are traditionally important numbers. it's the same reason why there is 108 stars (27 x 4). If you read a lot of ancient texts, regardless of source, there tends to be certain numbers that will pop up all the time, for various reasons. At this point the meaning is often lost, or devalued, but there are still examples of it, for instance, buildings in china often have no 4th floor because the character for 4 also means death, similar to how there is occasionally no 13th floor in a western building. It all comes down to various forms of astrology and mysticism.