This is the heading to His Wedded Wife in Plain Tales from the Hills (1888). It is attributed by Kipling to to 'Vibart’s Moralities' and collected as a Chapter Heading in successive collections, including Definitive Verse and the 2013 Cambridge Edition.
'Art thou the man ?' Perhaps an echo of 2 Samuel 12,7: 'Thou art the man'.
Cain murdered his brother Abel, Genesis 4, 8. See Kipling's poem "Cain and Abel".
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