The date of this work would place it at a point where Rembrandt had been working with the etching medium for a few years and was now starting to become more confident and ambitious in his techniques. One effect of this was to use a greater variety of tone, meaning he would incorporate very dark areas for the most important parts of the composition and then later use subtle changes in greys throughout the rest of the piece. In the case of this design, St Jerome Kneeling, the figure's back is shadowed darkest, with much more detail found to his right in a lighter fashion. There is also a good contrast between the bright light which cover the top half of the work and the shadowed area below. Rembrandt expands on this room a little, with elements of brick work and several of this man's possessions also included here.
Rembrandt would develop his drawing and etching methods over time, taking in ideas from other local artists with whom he spent time before then appending his own creative methods on top. He would eventually become somewhat secretive about some of his techniques, keen to protect the successful career that he was now forging. It was also his etchings that provided him fame and fortune during his own lifetime, and enabled him to finance a large collection of other artists' work for a number of years, prior to experiencing financial problems in later life. He had essentially built a brand using the prints from these etchings and they could be sold far and wide, spreading his signature into new markets for the first time.
The prints produced from Rembrandt's etchings have been dispersed far and wide but within the last century or so there have been efforts by the major art galleries and museums to acquire as many of these as they can, with most available at fairly nominal prices. The end result of this is that several galleries will have prints from the same series of work, just different iterations of them. The artist would normally write on the back of each print which edition of print it was, and how many of each were produced. This helps art historians massively in documenting this part of his career, which would otherwise be almost impossible. Several extensive catalogue raisonnes of the artist's work have been produced in recent years, and the overall artworks run into the thousands, when counting all of the different mediums in which Rembrandt was involved.