According to Catholicism, what particular truth will the great apostasy deny?

>_CCC_ 675 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 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. There are many Church teachings about the "Truth" taught by Jesus Christ in the gospel and other "Truth" handed by the Apostles as Sacred Tradition and deposited to the Church. Is there a Catholic teachings or explanation on what particular "Truth" where apostasy will be committed?