Seven shows up repeatedly in Scripture. It appears first with the seventh day of creation, threads through God’s cycles of appointments with mankind, and foreshadows the timing of Messiah Yeshua’s arrival as the Word become flesh and culminates with many of the symbols of the Day of the Lord.
Keeping the jubilee year with both crops and servants were an act of faith on the part of the people of Israel. It is difficult to live in freedom of liberty and it is so easy to fall into bondage and slavery. God set up a safety net to protect the people from permanent bondage and slavery and to protect the land from being over consumed and dried up.