This latter image signifies the dramatic interplay and interaction of the opposing forces in the dualistic world of manifestation, leading to their union, and ultimately to harmony in the universe. This fact is amply reflected in the symmetrical and regular form of the endless knot.
The intertwining of lines reminds us how all phenomena are conjoined and yoked together as a closed cycle of cause and effect. Thus the whole composition is a pattern that is closed on in itself with no gaps, leading to a representational form of great simplicity and fully balanced harmony.
Since all phenomena are interrelated, the placing of the endless knot on a gift or greeting card is understood to establish an auspicious connection between the giver and the recipient. At the same time, the recipient is goaded to righteous karma, being reminded that future positive effects have their roots in the causes of the present. This is because the knot represents a connection, a link with our fates, binding us to our karmic destiny. Not surprisingly, this is one of the most favorite symbols in Tibetan Buddhism, and often occurs independently on its own.
Since the knot has no beginning or end it also symbolizes the infinite wisdom of the Buddha.
This article by Nitin Kumar