Poet makes different beautiful things combined to describe the Spring's beauties. For example the first paragraph he used varied birds such as Nightingale, Lark to reflect arrival of the Spring. We all know birds' sound represents flower blooming of which a sign of the Spring comes.
The second paragraph he placed boy and girl as a metaphor of sweetness and purity description. Mr Black's emotion on Spring can be seen as well as reflected either human-like or creature-like.