Q. Why is God sometimes called “The Holy One, Blessed be He”?
A. In post-Biblical literature the Biblical names of God are normally only used in quotations and prayers. In other contexts the Divine names are synonyms. HaKadosh Baruch Hu – “The Holy One, Blessed be He” is one of the most common. It recalls a name used 39 times in the Book of Isaiah – K’dosh Yisra’el, “The Holy One of Israel” (e.g. Isa. 1:4).
Up to the 3rd century CE, God was generally referred to as HaMakom (“The Place” – i.e. He whose place is everywhere). Arthur Marmorstein (“The Old Rabbinic Doctrine of God”) says that when the daughter religion began venerating human beings as “holy ones” (saints), who were eventually accorded cultic status, Judaism countered by withholding the designation “holy” from even the most pious and learned people.
Hence R. Chiyya says in the Talmud (Ket. 103b), “On the day Rabbi (Yehudah HaNasi) died, k’dushah (holiness) ceased”. Yehudah HaNasi, who died early in the 3rd century, had been known as “Rabbenu HaKadosh” (Our Holy Master). From then onwards, Judaism insisted that there was only one “Holy One”, i.e. the Almighty, HaKadosh Baruch Hu.