This sermon was given July 3,1988, only a few days after Archbishop Lefebvre, together with Bishop de Castro Mayer, consecrated the four bishops and as a result, was officially declared to be excommunicated.
It's less than 20 minutes long and well worth listening to, perhaps especially for those who foolishly are looking forward to an SSPX agreement with Rome, but also for the rest of us as a reminder or to help understand perhaps where we came from. Far as that goes, this sermon could almost have been given yesterday.
Link