When Yaakov and Esav meet, Esav says 'I have much' ('rov') whilst Yaakov says 'I have everything.' ('kol') Esav shows that he is a man of physicality, never happy with his lot and always wanting more material possessions; he only has a 'lot' but wants more - even though he has 400 men with him. Yaakov, on the other hand, has all ('kol') since he has all the physical things he needs for serving HaShem; he's thus happy with what he has. The pasuk in devarim (28;47) says that we will sin 'because we did not serve HaShem with simcha and good spirit merov kol. (lit. from much everything)' What does those last words 'merov kol' mean? The answer is that the reason we will sin is because we take the 'kol' (happiness with our physical lot and focus on ruchniyus) of Yaakov and convert it into 'rov' of Esav in focussing on materialism and its comforts. Thus, the pasuk reads 'merov kol' - because we pollute the 'kol' with the 'rov.' The lesson? Be happy with one's physical lot, for its only importance lies in its ability to be used for spiritual ends.
[combined from stuff i heard from R Roberts and R Tatz].