There broke out a severe persecution of the Church

There broke out a severe persecution of the Church in Jerusalem, and all were scattered throughout the countryside of Judea and Samaria, except the Apostles. Devout men buried Stephen and made a loud lament over him. Saul, meanwhile, was trying to destroy the Church; entering house after house and dragging out men and women, he handed them over for imprisonment.

-- Acts 8:1b-8

Before Christ's second coming the Church must pass through a final trial that will shake the faith of many believers. The persecution that accompanies her pilgrimage on earth will unveil the "mystery of iniquity" in the form of a religious deception offering men an apparent solution to their problems at the price of apostasy from the truth. The supreme religious deception is that of the Antichrist, a pseudo-messianism by which man glorifies himself in place of God and of his Messiah come in the flesh.

-- CCC 675

(Art: Bartholomeus Breenbergh, The Stoning of Stephen, Dutch, 1632. Oil on panel. J. Paul Getty Trust.)