The Sefer Yetzirah only enumerates three elements ‘fire’, ‘water’ and ‘air’, even though in the Medrash, in the Zohar and in the Rambam they enumerate four elements: ‘fire’, ‘water’ ‘air’ and ‘earth’, because primarily there are three elements ‘fire’, ‘water’ and ‘air’ which themselves also include the element of ‘earth’. And the element of ‘earth’ is only revealed at a later stage [with]in them.
There is a well-known example that illustrates this; when one places a pot of ‘water’ to boil on the ‘fire’ and there is [room for] some ‘air’ in between it then builds up [a dust like earth particle which represents the] earth element which is submerged within. Similarly, it could be understood how the three strands of ‘Chessed’, ‘Gevurah’ and ‘Tiferes’ above also include everything within them and it is from them that Malchus is also eventually revealed. Therefore, from the Torah there are only three Brochos but afterwards the Sages of blessed memory added the fourth blessing.
