Hey Don, thanks for that, especially about the gens d'armes in Q1 and the abyss from heraldry, which is clearly the primary meaning at the end. I think you're right that 'pourpre' needs to be rendered in a different word from 'rouge' in the English, but I just don't think 'purple' has the right connotations. Purple blood just doesn't seem right to me; crimson has to be the way to go.
Hrm, I just wrote the wrong thing and cut it out. The brindelles des abimes--how could that belong to Christ? It sounds like it is in apposition to rouge péchés. It must suggest the poet's own sinful coat of arms, not unlike but less noble than the rivers of blood on Christ's back, which he is asking Christ to cover with his own bloody mantle. This gives point to the pun on 'abimes,' as sins are certainly the work of Hell (the abyss) as much as the escutcheon marking the poet's sinfulness.