"John is going to be a proxy. A substitute."
During their conversation, Eloise Hawking mentions to Jack the need of a proxy for Ajira Flight 316. As implied by Eloise, a proxy is much like a "substitute" for another person. As the Oceanic 6 must recreate the circumstances that led them to Oceanic Flight 815, the dead Locke's coffin is going to replace Christian's, although Locke must carry an object that belonged to Christian. Jack later receives his father's shoes from his grandfather, and puts them on Locke's feet. ("316")
As a result of failing to find a proxy for enough events of Flight 815, some passengers of Flight 316 were teleported back into 1977, while the rest remained in current day. The two flights were sufficiently similar for the plane to enter the window the Island existed in and crash, but not sufficient enough for all of the passengers to emerge in the same place. ("Lost: A Journey in Time")
Similarities between Oceanic Flight 815 and Ajira Flight 316
|Flight 815||Flight 316 ("316")|
Jack loaded Christian's body on the plane, wearing Jack's tennis shoes. ("White Rabbit")
Jack loaded Locke's body on the plane wearing Christian's shoes.
Jack had a heated discussion with a flight attendant at the airport about his father's corpse. ("White Rabbit")
Hurley had a heated discussion with a flight attendant at the airport about flight passengers.
Hurley read a Spanish comic book. ("Exodus, Part 2")
Hurley read another Spanish comic book.
Charlie carried his guitar. ("Exodus, Part 2")
Hurley carried a guitar case.
Kate was escorted by Edward Mars. ("Pilot, Part 2")
Sayid was escorted by Ilana.
Rose was holding on to Bernard's wedding ring.
("Pilot, Part 1") ("Walkabout")
Sun was holding on to Jin's wedding ring.
Hurley almost missed the flight. ("Exodus, Part 2")
Ben almost missed the flight.
Seth Norris replaced Frank Lapidus as the pilot for Flight 815.
("Pilot, Part 1") ("Confirmed Dead")
Frank Lapidus was the pilot of Flight 316.