"Game of Thrones" gets its name from the first book of George RR Martin's "A Song of Ice and Fire," and while the meaning of that song is a bit obscured, the polarity of Ice and Fire represents many of the main threads running through the story. Literally, the powers are conceptualized in the form of the White Walkers in the North and the dragons in the East, but more interestingly, they refer to two of our main heroes: Jon Snow of House Stark and Daenerys Stormborn of House Targaryen.
"Kill the Boy" focuses exclusively on characters in the North and around Meereen, so comparing the two young rulers gives us insight into the perils of command.