Taking into account the statement above "The Magna Carta was written in 1215, but by 1600 it was being interpreted very differently than its original intention. Identify the important issue at the heart of the new interpretation of this document."
The answer is: the interpretation that all the Englishmen had rights and freedom in that time.
The Magna Carta was originally established and made to bring peace to the conflicts by promising a series of "liberties" to "all the free men of our realm". Also, Magna Carta was helpful for everyone but the peasants and slaves because they didn't have rights.