Answer: it offers a counterclaim to the first stanza, which is then rejected in the third stanza.
This poem discusses the pain and difficulty of moving through life. The author states that he cannot still his heart but that, soon enough, when all the birds have flown, it will stop. The first stanza presents the problem, while the second one, by discussing the swallows and the skyward, offers a counterclaim. However, we see that in the third stanza, this is rejected. We can identify this because of the phrase "sweet delusion."