How we cite our quotes: (Line)
Quote #1
A Skylark wounded in the wing
A Cherubim does cease to sing. (15-16)
When a bird gets wounded, an angel gets hurt too—that's what Blake is saying. Since "all that lives is holy" (in the words of Blake's "The Marriage of Heaven and Hell"), a bird is as important in God's eyes as a human or an angel.
Quote #2
The Caterpillar on the leaf
Repeats to thee thy Mother's grief. (37-38)
This is a complicated one—apparently, the caterpillar reminds people of Eve, the "Mother" of humanity, whose sin in eating the forbidden fruit led humanity to fall from Eden. For Blake, the fall from Eden caused the creation of the natural world (which is really an illusion) and the descent of the spirit into lower life forms (like caterpillars, which feed off the natural world).