The workbox is a box the husband gives his wife to keep her sewing supplies in. He has made it from the same oak that was used to make the coffin of John Wayward. The wife is shocked by the news that John is dead, and the husband seems to enjoy the fact that his gift has had such an effect on the wife. He questions his wife about knowing John, and she denies knowing him, even though he was from his wife's home town. It is in the last stanza that we know that the wife did know John Wayward and has always loved him.
Yet still her lips were limp and wan,
Her face still held aside,
As if she had known not only John,
But known of what he died.
The wife's reaction to John's death is deeper than she wants to admit, and she tries to hide it from her husband.
The irony of the little workbox is that it is in effect a miniature coffin, and what the husband gives his wife as a present becomes its opposite—an occasion for pain each time she takes up her sewing. A more sinister possibility, of course, is that the husband knows the full story, or more likely that he suspects it, and has deliberately fashioned the workbox either as a test or as a punishment for his “little wife.” The deeper irony is that the husband, by his suspicions, is probably destroying forever any possibility of future truth and intimacy with his wife. The wife’s rejection of the husband’s suggestion that she is “shocked” is also ironic. Whether she makes the denial to preserve her mystery or to defend herself from further probing is part of the poem’s ambiguity.