Ibn Ezra on Leviticus 25:2

ושבתה הארץ שבת לה׳‎. מצוה על ישראלי שלא יעזוב גר לזרוע שנת השבת כאשר לא נעזבנו לעשות מלאכה בשבת כי הוא ברשותנו: THEN SHALL THE LAND KEEP A SABBATH UNTO THE LORD. There is a commandment upon the Israelite not to allow a stranger to sow in the Sabbatical year.¹⁰For Scripture tells us that the land shall keep a Sabbath unto the Lord. This is similar to the commandment that we not allow a stranger to do work on the Sabbath.¹¹See Ex. 20:8 and I.E.’s comments thereto (Vol. 2, p. 427). Scripture commands this, for the stranger is in our power.¹²Hence we can prevent him from working on the Sabbath and sowing during the Sabbatical year.

וטעם שבת לה׳‎. כיום השבת וסוד ימי עולם רמוז במקום הזה: A sabbath unto the Lord is similar in meaning to the Sabbath day.¹³The Sabbath day is also referred to as a sabbath unto the Lord (Ex. 20:10). The secret of the days of the world is alluded to in this place.¹⁴See I.E. on Gen. 1:5, “There is a secret meaning to the Midrashic statement to the effect that the world will exist for six thousand years” (Vol. 1, p. 33). Also see I.E. on Gen. 8:22 (Vol. 1, p. 119). Also see Sanhedrin 97a,b.