Shavuos is "Chetzyo Lachem, Chetzyo LaHashem". Interestingly, it seems that on Shavuos there's more of a reason to be involved in gashmiyus, because once we have Torah, gashmiyus can be raised onto the level of ruchniyos. That's why Shavuos is the only time during the year when chametz is brought as a korban - because with Torah, even the Yetzer Hara can be used for the right purposes.