Four short lines carry a surprising amount of tension. A group sits down to eat, but not at a table: they "dine on our knees," a posture that suggests kneeling, as if the meal were also a kind of prayer or ritual. They raise a drink to the speaker's "dead cook," so the meal seems to honor someone who once fed them. The title, "Tribute," fits that reading.
Then the poem turns inward. The speaker admits their mind is "taken up / with my own sin." Instead of fully focusing on the person being remembered, they are preoccupied with their own guilt. The poem doesn't say what the sin is, and that silence is part of its power. We can only guess, perhaps that the speaker feels responsible in some way for the cook's death, or simply that grief has stirred up guilt. That is an inference, not something the poem states.
The mood is quiet, solemn, and uneasy. A gesture of respect becomes something more private and troubled.