Some time after this, he was raised to the highest position in the Medici bank available to non-Medici: "General manager" (and was referred to by Lorenzo as nostro ministro).

They are invaluable for their full and honest statements of Sassetti's finances and for the light they shed on the internal workings of the bank when he was the general manager.

They also are interesting in showing how Sassetti made liberal use of interest-bearing deposits and reinvested his earnings from the Medici branches in other enterprises.

De Roover detects in the accounting methods of the libro segreto a growing distraction by Sassetti, who was increasingly interested in secular humanist activities.

It features a fresco cycle, dedicated to Sassetti's namesake, St Francis, as well as portraits of his family and images of contemporary Florence and an altarpiece on the theme Adoration of the Shepherds.