Elessar, who was Aragorn, who was Estel, has many people to remember. And to mourn. Chief among those is his kinsman, Halbarad, who fought at his side on the Pelennor Fields, and fell there in his service.
That loss, of all the brave men who died, grieved Aragorn the most. But over the years, as he has grown older, he has come to see that even had he known his fate in advance, Halbarad would nevertheless have chosen to fight. For such a man as he, it was no choice at all.
Halbarad was a soldier, after all, born and trained, and knew the danger he was facing when he came from the North to aid his friend and kinsman, never to return. The thought consoles Aragorn that Halbarad fell fighting, in all honor, with his men around him to ease his passing as best they could. He saved many lives by giving his own, and he must have known that before the end.
Aragorn takes comfort, also, in the knowledge that his brother in arms will not be forgotten. He has personally seen to it that many ballads have been written and songs sung of Halbarad's valiant deeds, at Pelennor and elsewhere. History will not forget Halbarad of the Northlands until the world is changed and all who knew him are gone and themselves forgotten entirely, and that is Aragorn's doing.
Thus he honors his friend, and preserves his memory as is fitting. His task complete to the best of his ability, he turns from the past and looks to the future. Soon, he will marry the Lady Arwen, and rule the kingdoms reunited - he hopes wisely and well - and lead his people into a time of peace.
It will not be easy. But whatever it takes, he will achieve his aim. And he will teach his heirs of the debt they owe to the sacrifice and courage of good men now gone. They will be remembered. Eternally.