Rashi: He toils for his need.

R. Yonah: Sometimes the Nefesh toils for Amal, i.e. the body, and not for itself. A Chacham is opposite. He toils for the Nefesh - "Imrei No'am Masok la'Nefesh" (24).

Rashi: When his mouth forces him and demands food, then his toil stands for him; he eats what he already toiled.

R. Yonah: The need of his mouth is heavy upon him. He seeks excesses and pleasurable foods and delicacies. Therefore, he needs to toil much. Achaf is heavy, like "v'Achpi Alecha Lo Yichbad" (Iyov 33:7) - my heaviness and burden will not be heavy on You.

Malbim: Is it possible that the Nefesh will toil because his mouth forces him?! The mouth that wants to eat, it forces the spiritual Nefesh to toil constantly - "Kol Amal ha'Adam l'Fihu v'Gam ha'Nefesh Lo Simalei" (Koheles 6:7). It clarifies for him this folly. The eternal Nefesh is primary in man. His primary life is eternal life, of the Nefesh. Man was created to live life of the Nefesh, via killing the body and its requests. Even though the path is initially full of thorns, he will find life in the end - eternal life after he returns to eternal pleasure. Is there any greater folly than for this dear Nefesh to abandon its spirituality, and toil for the needs of the mouth that wants to eat and drink "Achol v'Shaso Ki Machar Namus" (Yeshayah 22:13)?! Nothing will remain to the Nefesh for all its toil! The Sechel, which understands life of the Nefesh, its spirituality and its persistence after death. It says above "Evilim Yalitz Asham; Lev Yode'a Maras Nafsho;