Amos wrote "Spark" after suffering a miscarriage. She discussed the song in an article from Q magazine in May 1998.
Y'know, once you've felt life in your body, you can't go back to having been a woman that's never carried life. The other thing is feeling something dying inside you and you're still alive. Obviously when it was happening, it was already over, but in my mind, you don't know that it's over yet. You're doing anything, thinking, 'Oh God, maybe if I put a cork up myself, maybe it'll keep this little life in.' That's why in 'Spark', I say, 'She's convinced she could hold back a glacier/But she couldn't keep baby alive.' You just start going insane. There's nothing you can do, so so you surrender and then... start again.
The timing for an Amos release has never been better, as the mainstream has apparently caught up to the singer/songwriter's quirky brand of pop music. She meets fans halfway with this first single from the imminent, much-anticipated new album, From the Choirgirl Hotel, by infusing the song's complex, piano-driven structure with a sticky chorus and ample use of scratchy angst-rock guitars. Amos continues to explore the far regions of her vocal range, yelping and ranting at whim. However, she counters that with welcome softer nuances that serve the song well. Add an insinuating, tribalistic midtempo drum, and you have what could be a major pop breakthrough for this eternal critical darling. – Billboard (April 1998)
Amos requested the video for "Spark" to be directed by James Brown, who originally had a different idea for the video that Amos didn't like; she requested wanting something "where a girl has a will to live." The video was shot in Dartmoor, South West England and took three days to finish.
You don't really know what's going to happen to her, but that's not the point. She's trusting her instincts in a way she never has before, she's finding something in herself she never knew even existed. The man who's trying to find me, probably is the driver. You don't really know too much about him, but you know she's got to get away from him. The water shot – it was about an hour and a half. It was 5:30 at night, and the sun was going down. [switches to up-close shot where she wriggles from the blindfold] Here, right here, I'm in a different water tank, and they had me swimming around for a while trying to get close-up shots. [About the overhead shot where we see Amos running along the banks of the river directly after the water sequence] Well, that was my double, right there. She was walking in a forest while I was shooting all this, because it took hours to get those two seconds. I had changes of clothes – I had wet clothes and dry clothes, and in the middle of the forest the girls would stand around me in their parkas and I'm putting the wet clothes on and putting on the muddy clothes to get the right outfit at the right time. "Here [the car at the end], these two are brother and sister, and they're in the album artwork, where they look like angels in the artwork, although here they're very much like the Village of the Damned. You don't know what's going to happen to this girl, but she has a will to live.