Every Tear from Every Eye Becomes a Babe in Eternity. This is caught by Females bright And return'd to its own delight. (67-70)
A tear of real joy or sadness is something that will bear fruit in eternity. It's a sign of humanity and it can only develop into something more substantial and divine. This is what Blake means by calling it a "babe." The "Females Bright" who catch the babe and return it are mythological figures—they're like a positive version of the Fates from Greek Mythology. They're helping to weave the fabric of human destiny.