What is the comparison to grapes in the Midbar?
Rashi: Grapes are dear in the Midbar - so I cherished Yisrael.
Radak: A Midbar is dry, without any fruits. One who finds grapes there, he rejoices.
Radak citing his father: "Ba'Midbar" is connected to Matzasi. Like grapes and a newly ripened fig, which one who finds them rejoices, so I found your fathers in the Midbar, and I rejoiced with them.
Malbim: When I found your fathers in the Midbar, they were esteemed to Me like grapes - the most important fruits, in the Midbar, which is a place without seeded crops, vines and fig trees. This was the first vineyard that Hashem planted - "Gefen mi'Egypt Tasi'a" (Tehilim 90:9). Grapes cannot be grafted. Especially grapes in the Midbar are not grafted. So Yisrael are Kedoshim, and are careful to avoid Zenus. Shelumis bas Divri was the only one in Egypt who transgressed Arayos; the Torah publicized her (Shemos Rabah 1:28). 1
Malbim: After saying that they corrupted their ways with idolatry and Zenus in the days of Giv'ah, and therefore their sin was mentioned, it says that they should learn from a Kal v'Chomer from the punishment of Yotzei Egypt for the sins of Ba'al Pe'or and Zenus with Bnos Mo'av. That generation was esteemed and dear in Hashem's eyes. All the more so He will punish this generation for these Aveiros, for they are lowly and disgraced in His eyes!
What is "Bikurah vi'S'enah"?
Rashi: It is a ripe fig on the tree.
Why does it add "b'Reishisah"?
Rashi: It is at the beginning of ripening of figs. Radak - I rejoiced over Yisrael like one who finds a newly ripened fig. I financed them, and they did not lack anything, as if they were in a settled land, and they did not appreciate My good! The Navi mentions this, for the children did like the Avos. I benefited your Avos, and they rebelled against Me. So I benefit you, and you sinned against Me!
What did He see about Avoseichem?
Rashi: I viewed them like a newly ripened fig, to endear them.
Malbim: I viewed them as esteemed. Grapes are the most important fruits in the Midbar, and it is astounding to find them in the Midbar, but also figs are also important. There is no waste in it 1 . The first to ripen is more important, for few ripe ones are found then. So Yisrael were esteemed due to their place, like grapes in the Midbar, and the time when Divine influence first took effect on them, when darkness covered the nations.
Tanchuma Lech Lecha 21, Bereishis Rabah 46:1 - it has only a little waste, i.e. the stem.
What is the meaning of "va'Yinazru la'Boshes"?
Rashi: Nezirah always refers to separation. Boshes is idolatry - their shame.
Radak: They separated from Me to go after idolatry - those who serve it are ashamed of their deeds.
Malbim: This is like it says "va'Yochal ha'Am va'Yishtachavu lEi'loheihem" (Bamidbar 25:2).
In what way were they Shikutzim?
Rashi: They were disgusting in front of Me. Malbim - this is in spite of their initial importance. All the more so, Efrayim are disgusting to Me due to their sins!
Radak #1: They served Shikutzim when they loved Bnos Mo'av and were Mezaneh with them. Bnos Mo'av tilted Yisrael's hearts to serve their gods. It is as if it says va'Yihyu La'avod Shikutzim.
Radak #2: One who serves [idolatry] is Shikutz.
Radak citing his father: Like the measure of love that I loved them [initially, now] they were disgusting in My eyes.
What love is discussed?
Rashi: Their love for Bnos Mo'av.
Refer to 9:10:6:2.