Moses tells the Jewish people

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"If you work as laborers in the vineyard, you will be able to eat as much grapes as you want until you are satisfied." 

 In a wheat field and working in the vineyard characterize both aspects of our relationship with G-d.

Wheat, the fundamental ingredient of food, symbolizes the acceptance of G-d's sovereignty and the observance of His commandments.

Grapes, a nice supplement to basic nutrition, represent the relationship with God that is beyond the letter of the law.

When we have reached spiritual maturity sufficient to feel pleasure and joy at the revelation of the Divine, we seek to infuse the consciousness of the Divine in all aspects of our lives and not only those expressly required by the Torah.

The Torah allows field and vineyard workers to enjoy wheat and grapes during their work.

This teaches us that, whatever our degree of relationship with G-d -the level of "wheat" or the more noble one of "grapes" acquired by greater devotion to Him-we will always be rewarded by greater revelations. Divine and divine beneficence.

Speech of The Lubavitcher Rebbe,Rebbe Menachem Mendel Schneerson ,Likoutei Sihot,Volume 34,Page 129.