In a spiritual sense which is greater - or if you prefer, has more kedusha - angels or Jews and why? Please explain and cite explicit sources, not inferences.
this is well explained in Shaarei Kedusha part 3
here's some excerpts:
I will ask a few deep questions.... To know if the soul of man is greater than the angels or not. If we say that it is, then why didn't the angels also go down to this world to dress in a body? And if (you say) the angels are greater, this cannot be, because all the writings of the Sages we find the opposite. For example, "Who is greater the guardian or the guarded" (Midrash) and many others. Also, the bible itself testifies the opposite as it says "You have weakened, the Rock (G-d) that formed you" (Devarim 32:18). Or "Give strength to G-d" (Tehilim 68:35), "You are sons to the L-ORD your G-d" (Devarim 14:1). "Yisrael in who I am glorified" (Yeshaya 49:3), "the angels don't say 'Kadosh' until the Jews starts below." And we don't find such things by the angels at all anywhere (that we need to wait for them)
Now we have explained well what is man. He includes within himself all the worlds whether in the subdivisions or the totality of all the worlds, unlike all the other creations whether upper (angels) or lower (animals,etc.) which only include from the world in which they were created.
Now we have explained all the answers to the questions we posed above (beginning of Sec.III). Now, the light of the souls of men is more inner and higher then that of the angels, therefore the angels are his servants - because through him (man) they (the angels) receive their light and life from the 10 sefiros.
And therefore, the angels did not descend below to wear a physical body,because certainly they would be defeated by the klipos. Because even the souls of men does not have the strength to stand up to the klipos, all the more so them. And the proof is from the "Nefilim" (fallen angels in Bereishis 6:4 - Rashi on Bamidbar 13:33 brings down "Nefilim-Giants among the sons of Shamchazay and Azael who fell from heaven during the days of Enosh"), who tried to descend to this world and became lost. They will be destroyed in the future.