Albert Barnes on Luke 2:35

Yea, a sword (s) , &c. The sufferings and death of thy Son shall deeply afflict thy soul. And if Mary had not been thus forewarned and sustained by strong faith, she could not have borne the trials which came upon her Son; but God prepared her for it, and the holy mother of the dying Saviour was sustained.

That the thoughts, &c. This is connected with the preceding verse: "He shall be a sign, a conspicuous object to be spoken against, that the thoughts of many hearts may be made manifest"-- that is, that they might show how much they hated holiness. Nothing so brings out the feelings of sinners as to tell them of Jesus Christ. Many treat him with silent contempt; many are ready to gnash their teeth; many curse him; all show how much by nature the heart is opposed to religion, and thus are really, in spite of themselves, fulfilling the Scriptures and the prophecies. So true is it that "none can say that Jesus is Lord but by the Holy Ghost," 1Cor 12:3.

(s) Jn 19:25