The Haftorah of parshat Toldot is the beginning of Malachi. The book begins: The burden of the word of Gd to Malachi.” The chapter then goes to chastise and really “ream” the Kohanim who do not act properly and the people for bringing bad sacrifices. It even goes on to call sacrifices of the festival-feces.
Why is prophecy a burden. Why connect with the bad things the Kohanim are doing? THe Shikker Dovid would respectfully like to suggest that when one holds oneself to be a religious person, they hold themselves to a higher standard. More is demanded. If you wear a kepah, you must always offer your seat on the train. If you wear a kepah, you must make sure your “sacrifices” your ritual acts are not clouded with bad behavior. This is the burden and the connection to the Kohanim.