I love writing to film scores - to me they're the quintessential essay writing music - music that was composed to help tell a story! We know that familiar music is good for this purpose as it occupies less cognitive space and you can't get much bigger than the Harry Potter movies.
Alexandre Desplat is one insanely talented composer - aside from Harry Potter you'll hear his work in films like: The Tree of Life, The Imitation Game, Fantastic Mr. Fox and more recently in The Secret Life of Pets.
Lily's Theme is one of those tracks that sneaks up on you - soft to open - almost reminiscent of Howard Shore's work in Lord of The Rings - but then the strings kick in and the emotion starts to run wild - but not too wild - and before you know it, you're back down, fading out to quiet.
It's one of those tracks that you don't notice you've listened to until it ends - which is perfect for this kind of playlist.