from Dafydd Jenkins who says
“The reversal from ‘fine flour, barley’ to ‘barley, fine flour’ between verses 1 and 18 is a classic signal for an inverse parallel.
The centre of the pattern is two paired structures, however D has a b c, a b c, while D’ has a b c, c b a. D highlights the lepers recognition that they need to report God’s salvation, D’ that the king fails to believe the report.