It is written: "Six days shalt thou work and on the seventh day thou shalt rest, and cease from plowing and harvesting" (Exodus 34:21).
Why are plowing and harvesting specifically mentioned?
The answer given is that for six days one is to do God's work in the world.
This is avodah, or the imposed tasks of life which nurture existence outside of the Garden of Eden.
It is more than just tilling the soil.
It is a labor and an agony, a matter of drawing forth nourishment by the sweat of the brow.
But the real work of man is Divine worship, also called avodah.
In which category there is, again, plowing and sowing.
And then, there is harvesting.
Plowing is the first task, a matter of preparing the heart by breaking the hardened crust of the soil around it.
And also to make furrows of fresh soil, free of weeds and thorns, capable of serving as a bed for the seed.
Because, as is well known, no matter how rich the potential of the seed, it needs a soft and suitable bed of soil in order to sprout.
Many people often have spiritual experiences, or receive the grace of genuine wisdom through a written or spoken word, but fail to let it develop into anything productive because the seed falls on uncongenial stony ground.
On the other hand, we can point to numerous instances of individuals whose entire lives were changed because of a single phrase or sentence that pierced them to the core.
A person has been known to just open the Siddur (prayer book) at random and discover something that nourishes his soul for a lifetime. Often it is the result of seeing something familiar in a sudden illumination.
The work of sowing is connected with the receptivity of the heart.
Only too often the heart is open and ready to receive something truly significant, and what is absorbed in this readiness is a trivial make-believe of little value.
It seems to be a fairly universal error, to catch hold of a cheap trinket in an hour of great emotion-whether of fear, exultation, or love-and to cherish it as though it were a precious jewel.
Opening the heart and sowing the proper seed thus require care and discrimination.
Thereafter, there is the work of watering the soil, for the rains are not always to be relied upon, and then the task of weeding out the undesirable growths that spring up and threaten to choke the crop.
To be sure, in the work of Divine worship, the uprooted weeds and thorns may also be useful in their own way and are not alwaysto be discarded carelessly.
–Rabbi Adin Steinsaltz
From The Candle of God, "Hidden Aspects of Shabbat," by Rabbi Adin Steinsaltz