What is the sword?
Theolphylact of Ochrid: that is, grief because of our Lord’s passion passed through her soul, who although she saw Christ the very Son of God die a voluntary death, and doubted not that He who was begotten of her flesh would overcome death, could not without grief see Him crucified.
What are the thoughts being revealed?
St. Gregory of Nyssa: …] when all these events took place, there followed the discovery of many men’s intentions. For some confessed God on the cross, others even then ceased not from their blasphemies and revilings.
Or this was said, meaning that at the time of the passion the thoughts of men’s hearts should be laid open, and be corrected by the resurrection. For doubts are quickly superseded by certainty.
Or perhaps by revealing may be meant, the enlightening of the thoughts, as it is often used in Scripture.
Theolphylact of Ochrid: But now even down to the close of the present time, the sword of the severest tribulation ceases not to go through the soul of the Church, when with bitter sorrow she experiences the evil speaking against the sign of faith, when hearing the word of God that many are raised with Christ, she finds still more falling from the faith, when at the revealing of the thoughts of many hearts, in which the good seed of the Gospel has been sown, she beholds the tares of vice overshooting it, spreading beyond it, or growing alone.
Origen: But the evil thoughts of men were revealed, that He Who died for us might slay them; for while they were hidden, it was impossible to utterly destroy them. Hence also when we have sinned we ought to say, Mine iniquity have I not hid. For if we make known our sins not only to God, but to whoever can heal our wounds, our sins will be blotted out.
Taken from the
Catena Aurea.