The term “Jewish holiday” is etymologically derived from “Jewish Holy-day” and refers to days set aside for religious observance.
The Holy-days occur on the same dates every year in the Hebrew calendar. The dates vary in the Gregorian calendar because the Hebrew calendar is a lunisolar calendar (based on the cycles of both the sun and moon), whereas the Gregorian calendar is a solar calendar.
In the Kabbalistic tradition, Jewish Holy days ימים טובים are viewed as “celestial gates in time”. They are literally days when the visible planets are in specific alignments. These alignments are related to the Tree of Life.
They are moments in time when we have the opportunity to transform our souls.