JCoxeye's Leitmotif Index:
'THE HOLY'

Summary

'THE HOLY' is a seemingly very important motif, heard in only a few minor (but very important) songs, namely THE HOLY and flashback_excerpt.ogg.
The motif itself is split into two distinct halves:

('THE HOLY A', as heard in THE HOLY )

('THE HOLY B', as heard in THE HOLY )

Together:

('THE HOLY', as heard in THE HOLY )

Additionally, the motif has a backing melody:

('THE HOLY (BACKING)', as heard in THE HOLY )

Worth noting is that 'THE HOLY' may originate from a song Unrelated to Undertale and Deltarune - Penumbra Phantasm, as covered on the page 'On the Origins of Undertale and Deltarune's Leitmotifs'.