Swinburne, poet that he was, wrote his book length essay on William Blake in poetic language evoking emotions and calling on the intuition to assimilate the images presented. Here is his account of the beginning of Gates of Paradise (Page 19-23):
"In the first plate of the 'Gates of Paradise,' the woman finds the child under a tree, sprung of the earth like a mandrake, which he who plucks up and hears groan must go mad or die; grown under the tree of physical life, which is rooted in death, and the leaf of it is poisonous, and it bears as fruit the wisdom of the serpent, moral reason or rational truth, which invents the names of virtue and vice, and divides moral life into good and evil. Out of earth is rent violently forth the child of dust and clay, naked, wide-eyed, shrieking ; the woman bends down to gather him as a flower, half blind with fierce surprise and eagerness, half smiling with foolish love and pitiful pleasure ; with one hand she holds other children, small and new-blown also as flowers, huddled in the lap of her garment; with the other she plucks him up by the hair, regardless of his deadly shriek and convulsed arms, heedless that this uprooting of the mandrake is the seal of her own death also.
"Then follow symbols of the four created elements from which the corporeal man is made; the water, blind and mutable as doting age, emblem of ignorant doubt and moral jealousy ; the heavy melancholy earth, grievous to life, oppressive of the spirit, type of all sorrows and tyrannies that are brought forth upon it, saddest of all the elements, tightest as a curb and painfullest as a load upon the soul: then the air wherein man is naked, the fire wherein man is blind; ashamed and afraid of his own nature and its nakedness, surrounded with similitudes of severance and strife:...
"In these first six plates is the kernel of the book ; round these the subsecpient symbols revolve, and toward these converge. The seventh we may assume to be an emblem of desire as it is upon earth, blind and wild, glad and sad, destroying the pleasures it catches hold of, losing those it lets go. One Love, a moth-like spirit, lies crushed at the feet of the boy who pursues another, flinging his cap towards it as though to trap a butterfly; startled with the laugh of triumphant capture even at his lips, as the wingless flying thing eludes him and soars beyond the enclosure of summer leaves and stems toward upper air and cloud."
Blake expresses some of above sentiments about fleeting joys in this poem from his notebook (E 470) except those who release joys in this poem experience a higher level of existence:
"He who binds to himself a joy
Does the winged life destroy
But he who kisses the joy as it flies
Lives in eternity's sun rise"
Swinburne wrote 5 years after the Gilchrist biography was published, 41 years after Blake's death, and he wrote with the enthusiasm of a convert.
You can read Gilchrist's biography and Swinburne essays as Google books on your computer. Gilchrist's book is also available as a text document.
Here is Joseph Viscomi comments on the Gilchrist Life.
To learn more about Gilchrist and his book read on Wiki:
Volume II Blake's writings
Versions of Gilchrist's Book