Thanksgiving Day is a jewel, to set in the hearts of honest men; but be careful that you do not take the day, and leave out the gratitude.

Powell contrasts the outward observance of a holiday with the inward moral disposition it is meant to cultivate. Calling Thanksgiving “a jewel” suggests something precious and elevating—an occasion that can adorn and refine character when it is “set” in the heart. The warning that one might “take the day, and leave out the gratitude” criticizes empty ritual: feasting, leisure, and social custom without the reflective practice of thankfulness. The line also implies that gratitude is not confined to a calendar date; the day is valuable chiefly as a prompt to sustain a habit of appreciation, humility, and recognition of dependence on others and on providence.