Sometimes it’s not the whole song but just a moment.
Like the verses in “Grease is the Word” from Grease. The chords alternate between Bm and E before hitting F#m7 at the end of the couplet. Then the bass steps up to Em7 at “There ain’t no danger” and walks down to D and C. That Em7 (at :23 in the video below) hits me like honey:
Or the beginning of the chorus to “The Mixed Tape” by Jack’s Mannequin, which is preceded by an electric guitar sliding up to the climax of the chorus. The piano arpeggiates, tickling the ivories as it tickles my spine, McMahon crooning “Where are you now? / As I’m swimming through the stereo / I’m writing you a symphony of sound” beneath a fulsome ahh-chorus, starting at :29 here:
I didn’t choose these moments; they chose me. They burrowed into whatever deep part of the psyche finds transcendence important, however fleeting. “The Mixed Tape” is from a very specific memory, and I listen to it to evoke that time. “Grease is the Word” doesn’t fit in with the rest of the songs from Grease (which isn’t even close to my favorite musical), but for some reason I like it the best.
There is no explaining it.