Still life is, by definition, a painting featuring inanimate objects. The painting has a didactic purpose, in which each object becomes a symbol offered up for reflection. In this painting, the presence of the skull, which evokes the idea of death and opens up a reflection on life, is presented as a vanitas, integrated here with the fictitious portrait of a saint, enhancing the meditative dimension of the work.
The word vanity comes from the Old Testament and takes up the idea of "light breath". The theme of Vanitas in Spanish painting dates back to the importation of the Leyden school to Holland around 1620. The genre spread throughout Europe, to France, Italy and Spain.
The skull also evokes the part of the human skeleton where thought resides. By depicting only this anatomical part, it shows the carnal and ephemeral nature of the human body, and prompts reflection on memento mori, the moment of certain and inevitable death for all.
Here, Saint Jerome is holding the skull with both hands, as if to grasp death which, in the Christian religion, is seen as a passage, for those who have dedicated their lives to moral action, to heavenly life.