SISITH. — “Tassels” which, together with the gèdhilim (“fringes”), the Israelites attach to the corners of their outer garments (Num. 15:37–41); the blue cord by which the tassel of each corner must be fastened is meant to remind them of the Lord’s commandments. Deut. 22:12 enjoins the gèdhilim at the four extremities of the cloak.
The custom is very ancient; to us it seems to be a remnant of knot-writing. The blue may perhaps (as the ancient rabbis conjectured) have recalled the sky. It was a practice rigorously inculcated by the Pharisees (Matt. 23:5). In the Diaspora a special vestment began to be worn under the outer garment, reserving the blue thread and stripes for the mantle (tallith) to be worn during public prayers. The blue cord was abolished because it was originally of purple dye extracted from a worm, an industry that had fallen into disuse.