"Then do folk long to go on pilgrimage,..."
See in text (The General Prologue - The General Prologue)
Chaucer abruptly shifts from describing the natural world to describing folk going on a pilgrimage. While the flowers are blooming, the sun is shining, and the birds are getting busy, people are going on a pilgrimage, a religious journey to a sacred place. The juxtaposition of humans going on a religious journey and the lusty birds is meant to be humorous. This humorous beginning sets the tone for the rest of the poem.
See in text (The General Prologue - The Five Guildsmen)
"Chattels" meaning property or money. The "For" at the start of this line compares their riches to both their wisdom and ability to be an alderman, the head of a guild. In this way, Chaucer associates money with intelligence and power. Note that because of the tone of the General Prologue that this may be a satirical association.