This third "secret" is foretelling of all of God's people giving their lives in a massive self-sacrificial rite to gain entry into heaven in the final days in their Revelation prophecy. This is what they had planned for "The Bride" of Christ.
The third part of the secret revealed at the Cova da Iria-Fátima, on 13 July 1917.
I write in obedience to you, my God, who command me to do so through his Excellency the Bishop of Leiria and through your Most Holy Mother and mine.
After the two parts which I have already explained, at the left of Our Lady and a little above, we saw an Angel with a flaming sword in his left hand; flashing, it gave out flames that looked as though they would set the world on fire; but they died out in contact with the splendour that Our Lady radiated towards him from her right hand: pointing to the earth with his right hand, the Angel cried out in a loud voice: 'Penance, Penance, Penance!'. And we saw in an immense light that is God, something similar to how people appear in a mirror when they pass in front of it, a Bishop dressed in White. We had the impression that it was the Holy Father. Other Bishops, Priests, men and women Religious going up a steep mountain, at the top of which there was a big Cross of rough-hewn trunks as of a cork-tree with the bark; before reaching there the Holy Father passed through a big city half in ruins and half trembling with halting step, afflicted with pain and sorrow, he prayed for the souls of the corpses he met on his way; having reached the top of the mountain, on his knees at the foot of the big Cross he was killed by a group of soldiers who fired bullets and arrows at him, and in the same way there died one after another the other Bishops, Priests, men and women Religious, and various lay people of different ranks and positions. Beneath the two arms of the Cross there were two Angels each with a crystal aspersorium in his hand, in which they gathered up the blood of the Martyrs and with it sprinkled the souls that were making their way to God.