Sforno on Deuteronomy 26:3/ספורנו על דברים כ״ו:ג׳

1אל הכהן אשר יהיה בימים ההם, even if the priest in the particular generation may not be outstanding in wisdom, you must not therefore treat with less respect than his position warrants. This is why the Torah added the seemingly superfluous words לה' אלוקיך, words usually only used when addressing men of outstanding caliber such as kings and prophets. [If I understand correctly, the author mans that only high ranking people need to be reminded by implication that there is a higher authority than they themselves. Hence the addition of the words לה' אלוקיך after the word הגדתי. Ed.] At any rate, the idea is that seeing that the priest receives the bikkurim on behalf of G’d, it is as if G’d’s agent is addressed by the title reserved for his Master.

2הגדתי היום, equivalent to “I have made a public acknowledgment of the great works of the Lord today.” We find similar phrasing in Samuel II 19,7 when Yoav accuses David of having insulted all his ministers and generals by grieving over the death of his rebellious son instead of appreciating the loyalty of his followers who had saved his life under most difficult circumstances. The words there are: כי הגדת היום כי אין לך שרים ועבדים, “(by your excessive grieving) you have made clear that you do not consider that you have any loyal followers.”

3כי באתי אל הארץ, that I have come to this land from another country אשר נשבע ה' לאבותינו לתת לנו, as when G’d had said in Genesis 17,8 “I gave this land to you and to your descendants after you.” Seeing that G’d had sworn this oath at the time, I consider myself though apparently an outsider, a stranger, as if I am a permanent resident thanks to His gift, and this is why I have brought these choice fruit that it is incumbent upon anyone who has received the land as either a gift or even as a tenant to present to the real owner of the land in recognition of His largesse.