1. Shepherds we shall be For Thee, 'Boondock Saints'
There have been a few Boondock Saints references before, involving Rick and Daryl, so what better opportunity to throw in another one than when the two were on their whacky road trip adventure.
2. Jesus's introduction to 'The Walking Dead' was (pretty much) straight from the comics
Jesus is a character who will already be quite familiar to comic book fans, having been introduced back in issue 91. Despite the fact that his introduction was slightly different in the comics (where Abraham and Michonne were the first characters to come across him).
The final scene of the episode also bears a lot of similarity to issue 106 of the source material when Jesus breaks into Rick's house to talk to him, and finds him in bed with Andrea (yes, Andrea, see below for more on this character swap).