as the father of Elrond (Hugo Weaving's character) and of Elrond's brother Elros (1st king of Numenor) he stands for better or worse at the precise Mid-Point of the Legendarium.

(Which is fitting because the Old English ecclesiastical line about "Earendel over middengeard sendest" is something like the earliest literary spark for John to start writing in 1914)

As Earendil is in his late teens, the 1st age is on its last legs (to a later observer) but it certainly doesn't feel like it at the time!  Beleriand is over-run by Morgoth's forces almost everywhere except this huddling settlement at Sirion's mouths at the river delta.

And like the One Ring, the single Silmaril which Beren and Luthien won from Morgoth's crown is like a gift that keeps on giving to the antagonist, it's almost better left where it is as a wrecking ball to sow strife and division. 

As indeed after befalls: Elrond and Elros are six years old when the Havens are attacked by the four surviving sons of Feanor (two of which perish, the eldest and second-eldest sons of Feanor, Maedhros and Maglor survive the battle).  Elwing (the wife of Earendil) in despair bearing the Silmaril on her breast casts herself off the cliff into the sea but is rescued by Ulmo and transformed into a bird...then flies to Earendil's ship and -then- they take the Silmaril to Valinor.

Which...triggers the conditions for the Valar to advance their host to Beleriand and finally overthrow Morgoth and expel him from Arda. (which Ends the 1st Age)

so this...fever dream is for teenage Earendil to cast off his doubts.  Cirdan politely gives him his hour or two to daydream kind of knowing from experience that he'll change his mind.

Glad you gave my composition a listen.

--D