A man announces a journey with the calm of someone stating a plain fact: this morning he is leaving for Constantinople, where the woman he loves sells children's coats. The trip is simple, but the way he talks about it makes it feel like a small adventure. The city's old, grand name adds a touch of romance to what is, at the other end, an ordinary job.
The speaker's feeling comes through in the last two lines. He sent for his chest, meaning his trunk of belongings, and put on his black silk "for joy." Black silk is formal and rich, not what you'd normally wear to travel, so it shows how much this reunion matters to him. The mood is light, eager and tender. The poem is short and plainly worded, and that restraint makes his happiness feel sincere. Joy here is not shouted. It shows in the care he takes over getting ready.