What is the significance of planting wheat and thorns sprout?
Rashi: They prayed 1 , and their Tefilah was not accepted, because they did not fulfill "Niru Lachem Nir [v'Al Tizre'u El Kotzim]" (4:3), i.e. they did not repent.
Radak: The Nevi'im plant wheat in you, Yisrael, i.e. words of Nevu'ah; you are "Chelkasi" (verse 10 - My field). Thorns, i.e. bad deeds, sprouted. Yirmeyah used the metaphor of seeding a field, like Yeshayah (5:2) did - "va'Yitea'ehu Sorek... va'Ykan La'asos Anavim va'Ya'as Be'ushim." Yisrael are called Kerem Hashem and Chelkas Hashem (verse 10).
Radak citing his father: This is a metaphor for the masses of Yisrael sending to the kings of Egypt to help them against Melech Bavel. Their trust in this "broken reed" (Melachim II, 18:21) is reaping thorns.
Malbim: The Nevi'im planted wheat, i.e. words of Musar and rebuke that should sprout. However, they did not uproot the thorns and lusts from their hearts, and thorns sprouted, like above (4:3).
Rashi: Seforim in which there is a Chirik under the Zayin (Ziru is a command) are mistaken. (Rather, it is a Kamatz; it is past tense.)
What is the meaning of "Nechlu Lo Yo'ilu"?
Rashi: It is an expression of Choli (illness). They became ill with pains. Their cries in front of Me will not help.
Radak: The Nevi'im were grieved because their deeds did not help.
Radak citing his father: Yisrael were grieved [that they sent money to Malchei Egypt to help them against Melech Bavel, for it did not help at all].
Malbim: Afterwards, illness and afflictions came to make them return to Hashem - but also this did not help.
Are they ashamed of their crop?
Rashi: "Tevu'oseichem" refers to deeds.
Radak: The Nevi'im hoped that their crop would be wheat, but it was thorns. They became ill due to Hashem's anger, i.e. fear of His anger that will come on you due to your evil deeds.
Radak citing his father: This is a command. You should be ashamed of your crop, which is thorns.
Malbim: Be ashamed of Hashem's anger, which will double your afflictions.
