Avodah Zara 5b: (Tana d'Vei Eliyahu): One should bear the yoke of Torah like an ox, and make himself like a donkey to bear the burden.
Why the simile to an ox and to a donkey?
Maharal
When an ox engaged in the work of pulling a plow or a donkey carrying a load, the exertion weakens their entire body. Also, one that is fully involved in Torah study invoking their intellect (perhaps missing meals) weakens the body.
Iyun Yaacov
An ox and donkey do their work for their master without thought a reward, so too should one study Torah and do Mitzvos without thought of reward.
Aderes Eliyahu
An ox bearing a yoke is symbolism for Torah study; a donkey carrying a burden symbolizing the performance of Mitzvos.
Gr”a (Mishlei)
One who provides services for those that learn Torah is like the donkey carries the burden; on that provide financially for a Talmid Chachum so he and his family do not lack, is like the ox within the yoke.
Gr”a (2nd)
Two levels of learning: those that learn the basic, pshat level are like the donkeys that able to carry great burdens; the other level delves into the Torah through pilpul who are similar to oxen that gore.
Shem MiShmuel
An ox and donkey have two distinctly different traits. Although an ox appears to be a proud animal and is adorned with horns, it still accepts a yoke upon itself and goes to work. A donkey is a lowly animal, but it, too, accepts its work happily. Similarly, a person should realize that he must have these two traits when he learns Torah. These animals are examples of the work ethic which a person should apply to his learning.
Chasam Sofer
Those that delve deeply into a Torah matter are like oxen that plow a field and then plow the row again. The field is prepared but the produce is not ready to be eaten. Others that learn broadly and apply the subjects to daily life are like the donkeys that carry a finished product.
Avodas Avodah
Learning Torah directs a person into the purpose of life and away from death, just like the ox plows a field a line at a time, concentrating on what lies in front and not worrying about what is over the next hill. However, the Torah learner (like the ox) does receive benefit from the work, pride of accomplishment. Therefore, the Torah learner also needs the experience of the donkey that carries the load without any benefits.
Chafetz Chaim
An ox is used in the production of crops (plowing); a donkey is used in transporting the harvested produce. Both labors are necessary for Torah. One must first labor to “produce” the Torah, to understand its complexities. Then, one needs to “carry” the Torah (constant review and application) to others to acquire this “produce”.
אשריכם זרעי על כל מים משלחי רדל השור וחמור (ישיעהו לב, כ)
Fortunate are you who sow upon all waters, who send forth the feet of the ox and the donkey
Fortunate is Israel for when they engage in studying Torah and bestowing kindness their evil inclination is delivered into their hands, and they are not delivered into the hands of their evil inclination.
The Jews chase away the evil inclination which comes, as if on its own feet, to corrupt man (Rashi)
Maharal: the ox symbolizes the evil inclination toward idolatry (as manifest by the Golden Calf). The donkey symbolizes the inclination towards illicit relationships. Sewing is a metaphor for charity, while water represents Torah study. Thus, the two meritorious acts of kindness and Torah study are protection against the two main actions of the evil inclination.
