While it is unknown why Heo chose to pursue medicine, his social status as a chungin may have prevented him from becoming a civil or military officer like his father.

King Seonjo rewarded Heo for his allegiance and his second successful treatment of the afflicted Crown Prince by promoting him to the senior second rank in 1596.

During this time, King Seonjo ordered Heo to write a medical book for his people, who suffered in the post-war period from epidemics and famines.

He wanted to publish a book promoting preventative care, detailed drug formulas, and treatment methods that commoners with little or no education could easily access and comprehend.

The work spread throughout East Asian countries like China, Japan, and Vietnam, where today it is regarded as one of the classics of Oriental medicine.

The chapter on "External Medicine" explains how the skin, muscles, blood vessels, tendons, and bones allow for movement and maintenance of posture.

Although Heo Jun worked extensively with the royal family, he emphasized making treatment methods accessible and comprehensible to common people.