It was made because he was the most famous preacher of his time and is believed to have preached to the most people of all other preachers of his era. He was so famous and important that Lorenzo actually became the most popular name in the United States according to the 1850 census. He led missions across the US and preached everywhere.
It is worth studying today for various reasons. For example, the engraving can be studied from an artistic perspective through things like form, content, style, and similar. It can also be studied from a sociological or anthropological perspective because of how he spread religion across the United States. It can also be studied as a part of history.