People pay the doctor for his trouble; for his kindness they still remain in his debt.

Seneca distinguishes between a professional service that can be compensated and a moral gift that cannot be fully repaid. A physician’s “trouble” (skill, time, labor) belongs to the realm of contract: money can settle that account. “Kindness,” however—humane attention, compassion, and personal concern—creates an obligation of gratitude that exceeds market value. The saying reflects a Stoic ethical emphasis on intention and beneficence: what matters most is not merely what is done, but the spirit in which it is done. It also critiques reducing human relations to transactions, insisting that genuine care establishes enduring social bonds and duties.