They commit to a lifelong process of "updating" their vows as they grow and change.
Lily vows to always tell Marshall when he has green stuff in his teeth. [S9E22] The End of the Aisle
In a pivotal series moment, Robin attempts to flee the wedding and literally crashes into The Mother. They commit to a lifelong process of "updating"
: Ted reveals he retrieved the locket from Central Park Lake but gives it to Barney so Robin will believe it came from her groom. : Ted reveals he retrieved the locket from
: Robin walks down the aisle to an instrumental version of "Sandcastles in the Sand," the song that first sparked her romance with Barney.
Future Ted closes the episode by noting that while no one can vow to be perfect, they can promise to love each other with everything they’ve got, because "love is the best thing we do". The End of the Aisle | How I Met Your Mother Wiki | Fandom