Thanks to Mark for the link to this article:
Turns out patients with aphasia, a condition that causes a person to have difficulty recalling words and putting them together in speech (often the result of a stroke or brain damage), can find help regaining the ability to speak through song. Music is a function of the right half of the brain, while plain speech is a function of the left half.
Perhaps by engaging both halves of the brain, singing words (as opposed simply to speaking them) causes you to remember them. Any child who's learned to sing his ABCs (or any adult who has to sing the jingle to himself to figure out what comes next in the alphabet) knows this.
So it's little surprise that a chanted and sung liturgy sticks in your head. Like it or not, when you sing sacred Scriptures, as we do in the Divine Liturgy, you're memorizing scripture. Nearly all the catechumens know the Words of Institution by heart. And they've never even spoken them in the service, just heard them chanted. (For a test, ask junior high kids who only hear the Words of Institution spoken, not chanted, if they know them by heart.)
The unknown hymnwriter said it well:
Lo, the apostles' holy train
Join Thy sacred name to hallow;
Prophets swell the glad refrain,
And the white-robed martyrs follow,
And from heav'ns with set of sun
Through the Church the song goes on. (LSB 940, v.3)