Brochas Daf Hei amud aleph

"Amar Reb Zeira ... HKBH is not like Boser v'Dam. When man sells a (precious) article, he is sad and his friend happy; but when G-d gave Torah to Bnei Yisrael he was happy."

The Gra points out the lack of a parallel. The seller of an object, no longer has the use of it; by contrast HKBH can continue to learn Torah.  The answer he suggests is that once Torah is given to mankind, even when G-d toils in learning, the Halacha is still determined by man, as the Gemara says in Psachim Kuf Yud Zion, "Elazar bni omer."

Furthermore, the upper world needs the lower world, just as a father cannot procreate without a mother. Torah has been given to us to sow and plough, and its form is determined by the way in which the workers, the Talmidei Chachomim, work.