The Devil had he fidelity — Devil's Advocate

The Devil-had he fidelity 1
Would be the best friend-
Because he has ability-
But Devils cannot mend-
Perfidy is the virtue 5
That would but he resign
The Devil-without question
Were thoroughly divine
(F.1510/J.1479)
[1] Devil:: devil's advocate, one who argues against the canonization of the candidate of a saint. Promoter of the Faith.
[3] ability:: the ability to find out the truth of the candidate.
[5] Perfidy, virtue:: he must keep skeptical, perfidious to the candidate.
[7, 8] Devil, divine:: the advocate, who is assigned by the Church authorities, must be thoroughtly divine himself.