The Hebrew for count or counting is sefirah (סְפִירָה). It’s the verb used in the verse in Leviticus that commands us to count the seven weeks. It’s also the term used to describe the ten divine emanations or attributes in the Jewish mystical system of Kabbalah.
The idea of sefirot as mystical elements begins in Sefer Yetsirah (The Book of Creation), which was likely written in Palestine between the 3rd and 6th centuries.
Over the centuries, the understanding of sefirot evolves in Jewish mysticism, until it reaches its fullest expression in The Holy Zohar, attributed to Rabbi Shimon bar Yochai, but “discovered” in 13th-century Spain by Moshe de Leon.
The Zohar quickly became the canonical text of Kabbalah. The ten sefirot are often depicted into a tree growing doward from its roots or the divine archetype of a human being. The mystical system now associated with the practice of Sefirat HaOmer or Counting the Omer is based on the writings of the disciples of Rabbi Isaac Luria. The ARI, lived in Safed in the 16th century and is considered the father of contemporary Kabbalah.
While the counting is simple, the path of spiritual growth is more complex. Kabbalists aligned the 49 days with the seven lower sefirot, or divine emanations: hesed, gevurah, tiferet, netzach, hod, yesod, and malchut.
Each of these attributes of G-d, in English – loving-kindness, power, beauty, victory, glory, foundation, and majesty became associated with both a week and a day.
So the first week is the week of hesed, the second week is the week of gevurah, etc. In addition, each day is associated with one of the seven lower sefirot, so the first day of each week is hesed, the second day, gevurah, etc.
Therefore, when we map it out, we can see more clearly in a 7 x 7 grid that each of the 49 days has its own particular combination of attributes, that can allow us to focus our intention and meditate on an a combination of attributes.
The first day is then hesed sheb’hesed, with loving-kindess, there is loving-kindess.
The second day is the aspect of gevurah sheb’hesed, within loving-kindness, there is power.