Hemingway, perhaps, penning article, becomes serious (7)
I believe the answer is:
earnest
'serious' is the definition.
('earnest' can be similar in meaning to 'serious')
'hemingway perhaps penning article' is the wordplay.
'hemingway perhaps' becomes 'ernest' (Ernest Hemingway).
'penning' is an insertion indicator.
'article' becomes 'a' (indefinite article).
'ernest' going around 'a' is 'EARNEST'.
'becomes' acts as a link.
(Other definitions for earnest that I've seen before include "Serious; pledge" , "Nearest (anag.)" , "Firm" , "Serious - advance" , "Something of value to bind a contract" .)