108 beads on a Mala necklace is sacred for a number of reasons:

MOON: The average distance of the Moon from the Earth is 108 times the diameter of the Moon.

1, 0, AND 8: Some say that 1 stands for God or higher Truth, 0 stands for emptiness or completeness in spiritual practice, and 8 stands for infinity or eternity.

HEART CHAKRA: Chakras are the intersections of energy lines in the body, and there are said to be a total of 108 energy lines converging to form the heart chakra. One of them, leads to the crown chakra, and is said to be the path to self-realization.

DESIRES: There are said to 108 earthly desires

TIME: Some say there are 108 feelings, 36 related to the past, 36 related to the present, and the 36 related to the future.

PLANETS AND HOUSES: In astrology, there are 12 houses and 9 planets. 12 times 9 equals 108.

SUN AND EARTH: The diameter of the Sun is 108 times the diameter of the Earth. The distance from the Sun to the Earth is 108 times the diameter of the Sun