"Ratio Quique Reddenda" - what did Sweerts mean?

The Portrait of a Young Man, or Self-Portrait, by Michael Sweerts, remains poorly studied, although this is one of the two known works, dated by the master himself, and dated 1656, a pivotal year in his biography. Beside the date the sheet pinned to the green tablecloth displays the signature and the moralizing motto: Ratio Quique [sic!] Reddenda. Titled as "The Bankrupt" the painting appeared in the collection of I. I. Shuvalov and with this apparently false title went first to the St Petersburg Academy of Arts, then to the Hermitage. The reading of it as belonging to the vanitas genre also leads away from the point. That the Young Man is not a frivolous embezzler, but a calculating businessman follows from parallels in Flemish and Dutch art. Neither is he a "melancholic", however similar his posture may be to many of them. The key to Sweerts' message is the Latin pinacogram, of which each word is capitalized and one is spelled in a somewhat extravagant manner (dat. quique). Rationem reddere evokes associations with the Gospel debt parables. Flemish painters had turned to this subject already in the early 16th century; Van Hemessen's depiction of the Unforgiving Slave is likely to be one of Sweerts' direct sources. The parallelism of earthly and heavenly "banking" is emphasized in Th. Halle's engraving Redde rationem being part of Veridicus Christianus by J. David. The engraving and the portrait have a number of details in common, and the relative comment abounds in references to the debt parables. The Young Banker of the Hermitage portrait puts aside his counting and muses that the same debit-credit law operates in the other world, and that the list of debtors includes every one of us: to get that message across was so important to the fanatically catholic Sweerts that he styled the Latin inscription as the title of this list.