There is nothing which is quite so bittersweet as nostalgia. It seems to cause a longing which is as intimate as the sound of blood pulsing to the brain.
Nostalgia is often linked with 'a longing for home' (and some people say with 'a longing for God'). It is a constant theme for writers like Hermann Hesse. Hesse's fairy-tales are littered with references to an elusive return to a 'home', often symbolized in a mother figure. His writing is quite haunting because of this. Can home be found in the past then? Or is it an attempt to return to a mythical Eden which is now guarded by an angel with a sword?
In Christian circles, people will often look down on those who indulge in nostalgia. There's even a scripture quoted to defend this perspective, from the great apostle Paul: "One thing I do: Forgetting what is behind and straining toward what is ahead, I press on toward the goal to win the prize for which God has called me heavenward in Christ Jesus."
This was from the same Paul who would continually tell those who would listen to him, about what he was like in the past and about his road to Damascus experience. Maybe he didn't think about his past excessively. But I like to think that later on, locked up in prison, with time on his hands, he finally thought more about his childhood and the people he used to know at the start of his 'race'. After all, when did Paul's race really begin?
We can never go back, no matter how much we may wish to, and that is the bitter part. Those moments from childhood which were good and happy can't be returned to. Unless someone invents a time machine they are going to remain as memories. Maybe they are romanticised anyway. The past is safe, secure, a place of refuge. The fears and the pain of those times can be forgotten or minimised.
But the sweet part is in the possibility of a meaning behind those events. Whether it is a first crush, or music, or a half-forgotten computer game, or a film, or a favourite old story - these things can have a meaning. They were character-forming events which have been given significance by us. There may well be a meaning beyond that - why would they leave such a lasting impression otherwise?
In the meantime, the events which take place now may be the cause for future nostalgia. And the present, as scary as it can seem, will also appear safe in the future.