Infant Joy

'I have no name;
I am but two days old.'
What shall I call thee?
'I happy am,
Joy is my name.'
Sweet joy befall thee!

Pretty joy!
Sweet joy, but two days old.
Sweet joy I call thee:
Thou dost smile,
I sing the while;
Sweet joy befall thee!

Blake must have been thinking about a passage in Spenser's The Faerie Queen when he wrote this. If you click this link, you come up with a google copy of Blake and Tradition by Kathleen Raine (Amazon offers this book for $50, but you have to persevere in your search for that). However google seems to offer a lot of access to this book, one of the first and best Blake books I found.

In Spencer's story there were thousand thousands of these infants, and the "keeper of the northern bar" admits them one by one. Raine sees here Urthona/Los. Relate this passage in Spencer to The Arlington Tempera, and you get a glimpse of Blake's total myth: the unborn coming down the northern passage, where the babe is clothed with flesh and mortality for a sojourn in the Sea of Time and Space; at the conclusion of mortality one arrives back on terra firma prepared to ascend the southern passage to the realm of Eternity.