The verse is a hexameter in the classical dactylic metre, internally rhymed (-orum, -orum) and chiastic (with symmetric word order) to add intensity.
The hexameter, which Arturo Graf in 'Art of the Devil' says is added sometimes to the 'Hymn of the Bell,' is designed to provide conclusion and perspective, through contrast with the trochaic verses.
Trochaics "I praise the True God, I call the people, gather the clergy. I lament the departed, banish plague, ornament feast days." etcetera
Laudo Deo verum,
Festa decoro. +6 more lines
"and sometimes, at the end , the fearful line;"
Est mea/ cunctor/um : ter/ror vox /daemoni/orum
The two rhymed words (-orum, -orum) add emphasis to the terror vox at the centre of the chiasmus.
Compare the simple Chiasmus in Virgil underlining the descent into Hell, "sola sub nocte" under the lonely night.
From the twelfth Century a classical Hexameter (posh poetry) was sometimes used to contrast with trochaic and iambic couplets and triplets (popular, or vernacular, verse). And another example of a single (late) hexameter, internally rhymed, is the verse on Bede's tomb:
Hac sunt infossa : Baedae venerabilis ossa.
Another hexameter (swallowing an excess syllable through crasis) from BL Arundel 83 f 126r complements a simple poem:
Equitas judicii: Eternitas regni.
Resurrectionis novitas: Ascensionis libertas.
Constantia in cruciatu: Victoria in conflictu.
etcetera +3 couplets; having a rubricated hexameter, with 'mei' counting as a single syllable:
Pellican/us di/cor : pro /pullis/ scindit/ mei cor.
In another example from BL Arundel 83 II, only a fragment survives in the rubric (12 types of human attitude), but an elegiac couplet provides the proem to the hard-hitting Ages of Life.
(Rubric) Duodec/im [proprietates] condici/onis hu/manae.
(Proem) Hac ratio loquitur : homini sic ut videatur
Quid sit; quid fuerit; quid-que futurus erit.
'Here reason speaks thus to man so that there may be seen: What is, what was, and what shall be.' Which is followed by vernacular trochees: Age Five, Youth, uses uses Chiasmus to show self-confidence in the face of cynicism: [Edit:the 'O' possibly, error for 'Q'= Quam]
Reason: Than proud crops withered, surely there is nothing more disappointing?
Youth:Nature's bloom, I rejoice in my youthful elegance.
Ratio: O siccis herbis : Ens vilior num superbis.
Iuvenis: Nature decore :Juvenili gaudeo flore.