Sanhedrin 103a: This refers to Achaz (who prevented Avodah and study of Torah.

Rashi: He does not review the text of his learning.

Malbim: Refer to 24:30:2:1.

R. Yonah (33): Surely this is a Mashal. We already know that if one will be lazy and not plow his field and work his vineyard, thorns will sprout over all of them. ¹ Because desire is from physicality, the Mashal for it is a field. Some land is easy to work, and some is hard; one seeds in it only via great toil. Even so, he will not abandon it to lose; he toils in the entire field to plow and water, until his field is properly worked. So with Nefashos - some have strong desire and harsh Midos, but when he works to fix them and draw them after intellect, they straighten, and despise evil and choose good. His heart is faithful and desires Avodas Hashem. Just like the land needs plowing, watering and seeding, the Nefesh needs similar matters. Plowing is constant rebuke of oneself. Or, a Chacham rebukes him, and he is humbled via Musar to break the hard heart, amidst Yir'as Hashem. Refer to 24:31:1:3, 21:4:3:3 and the note there.

Orchos Tzadikim (Sha'ar ha'Atzlus DH ha'Atzlus): An Atzel's Chachmah is compared to his field. Not only does it not grow grain because he does not work it properly - rather, it grow inferior matters, like thorns that damage.

Malbim: A field needs much work - one must plow, seed... An Atzel does not work it amidst laziness. A vineyard, which is already planted, does not need so much work, only to guard it, lest it be ruined. An Atzel will do this. However, a Chasar Lev does not understand the loss that will come to his vineyard if he does not guard it, and he slackens his hands also from the vineyard.

Sanhedrin 103a: This refers to Menasheh (who erased Hashem's name and destroyed the Mizbe'ach).