The Ramban says that Shmita and the Yovel cycle are fundamental mitzvos. Something is lost on us today – slavery has mostly vanished from earth, and Shmita and Yovel have long been missing large chunks of their key halachos for thousands of years.
Consider the fact that when the Ramban classified it as fundamental, Yovel hadn’t been properly marked for centuries. What about it is fundamental when the laws associated with it seems so antiquated, archaic, and arguably irrelevant?
The Pnei Yehoshua explains that Yovel is not just a time when slaves go free – it is a Yom Tov that celebrates freedom and liberty. The Sfas Emes notes that the nation was born by being liberated from the crucible of Egypt.
After millennia of exiles, restrictions on movement, bans, pogroms, genocide, and general oppression, society has developed to give all people human and civil rights; Jews can now practice Judaism relatively freely, to the extent that younger people today have little idea of what not being free means. While progress is undoubtedly a good thing, we must be vigilant not to take our rights for granted.
One of the brachos said daily is שלא עשני עבד – perhaps this alludes the principle that we do not take our unprecedented liberties for granted.
Yovel was dedicated to displaying our gratitude that we are always able to serve God – indicated by the shofar being blown. It becomes abundantly clear why it is classified a foundational mitzva; freedom is a wonderful thing that we are very grateful for. But moreover, perhaps it shows that even under oppression, slavery, and exile, we are nonetheless subjugated exclusively to God.
The soul always remains free.