Commentary Par XIII 40-41

Exactly what is referred to by these words is much debated.  See the summarizing treatment offered by Giacalone (DDP Giacalone.Par.XIII.37-45), which offers the following sense of the matter in dispute.  Christ redeemed, with his death on the cross, sins committed either (1) in the past or in the future; or (2) before His life on earth and after it; or (3) before His flesh was pierced on the cross and after the Crucifixion.  While it seems that the third of these alternatives is the most appealing (because it builds on the parallel structure of the entire passage, moving from Adam's rib to Christ's wounded side), it is also true that all three interpretations cause similar reflection: Christ died for our sins.

According to Schwarz (Schw.1966.1), pp. 147-48, these lines reflect the opinion of Peter Olivi (against the account found in John 19:30) that Jesus was pierced by the lance while he was still alive.  Schwarz believes that [Par XXXII 128] reflects the same understanding.  For the view that Dante was deeply aware of Olivi's work and essentially agreed with it, but never mentions his name because the Franciscan was being vigorously attacked by Church officials in Provence, who managed to have his Lectura super Apocalypsim condemned, see Manselli, 'francescanesimo' (ED.1971.3), p. 16.