Sforno on Exodus 23:17/ספורנו על שמות כ״ג:י״ז

1שלש פעמים בשנה יראה, to give thanks to the Lord for the attainment of freedom from bondage, in spring, in summer and in fall. All our achievements stem from Him.

2אל פני האדון, to appear in the presence of the אדון. The term אדון is applied to someone who is in control of perishable things, mortals, etc. The Torah, by using this name of G’d, reminds us that He is the master of the people who present themselves each as an individual. When they make such an appearance before the Lord, they are as if each making an obeisance before his Master. This “Master” is simultaneously the master of the soil they toil which provides their livelihood, seeing that G’d is on record as כי לי כל הארץ כי גרים ותושבים אתם עמדי, “all of the earth is Mine for you are strangers or at best resident strangers with Me.” (Leviticus 25,23). In view of the above, it is clearly appropriate to express our gratitude to Him during the three aforementioned seasons. Therefore, (19) ראשית בכורי אדמתך, a reference to the choicest of our respective fruit. The word ראשית is used in the sense of “the choicest,” in Amos 6,6 וראשית שמנים ימשחו, “they anoint themselves with the choicest oils.” Similarly, Amos 6,1, נקובי ראשית הגויים, “you notables of the leading nation.” The products qualifying for this commandment are the 7 listed in Bikkurim 1,Mishnah 3