In general, the various stewards and prefects, including the cook, should maintain a joyful mind, [a motherly heart], and a great [and vast] mind whenever they perform rituals or engage in work.

So-called joyful mind is the spirit of happiness. You should consider that if you were born in a heaven, you would be attached to pleasures without cease and would not be able to arouse the thought of enlightenment. Practice would not be feasible. Even less would you be able to prepare meals as offerings to the three jewels [Buddha, Dharma and Sangha]! Among the myriad dharmas, the most revered and precious are the three jewels. The most superior things are the three jewels. Indra cannot compare. A wheel-turning king does not equal them. The Rules of Purity says, "Revered by the world, it is an excellent space outside [worldly] things; pure and detached, the assembly of monks is best." Now we have the good fortune to be born as human beings and to prepare the food that these three jewels receive and use. Is this not of great karmic significance? We should thus be very happy.

Again, you should consider that if you were born into the realms of hell, hungry ghosts, animals, anti-gods, and the like, or born in circumstances where you suffered from one of the eight difficulties [such as being born in a place or time where the Dharma is not practiced or taught, being born without the faculties that would allow us to practice or locked into the views of social conventions], even if you sought to cover yourself in the power of the sangha, your hands would naturally be unable to prepare pure meals as offerings to the three jewels. Relying on that painful physical form you would receive pain and be bound in body and mind. Now, in this life, you have already prepared those meals. How happy a birth! How happy a body! It is the good karmic result of kalpas vast and great. It is merit that cannot decay. When you prepare food and cook it you should do so with the aspiration of taking tens of thousands of births and concentrating them into this one day, this one time, that you may be able to bind together in good karmic result the bodies of millions of [past] births. A mind that contemplates and understands things in this way is a joyful mind. Truly, even if one takes on the body of a wheel-turning holy king, if one does not prepare meals as offerings to the three jewels, in the end it has no benefit. It is only of the nature of water, froth, bubbles, or flames.

From: Tenzo Kyokun - Instructions for the Cook by Eihei Dogen -

Translated by T. Griffith Foulk [with additions by Yasuda Joshu and Anzan Hoshin]