You make some serious mistakes.

First, the concept of "sola scriptura" is not biblical. It is found nowhere in the Bible. Protestants are confused, heretical Catholics. The Catholic Church assembled the Bible under the authority of the Holy Spirit that was given by Jesus to the Apostles and their successors in Communion with the Vicar of Christ. The Revealed Word is both Written (Scripture) and Spoken (Tradition; Magisterium of the Church).

Now, as to the notion of "the Warning" or "Illumination of Conscience", this has been part of approved private revelation for centuries. The Holy Spirit is active even now and must be discerned. Some commentators even think "the Warning" corresponds to the breaking of the Sixth Seal mentioned in the Book of Revelation. It will be an act of Mercy prior to the arrival of God's Justice. It will rival the Miracle of the Sun at Fatima. Following this public Warning, the Atheists are not going to have an excuse for continuing in disbelief. But some commentators feel that the False Prophet will attempt to explain away this supernatural act of Mercy as purely material in origin. This act of defiance in the face of God's Mercy is what will bring about the supernatural destruction of the False Prophet and the Beast (materialism and the followers of materialism) and will usher in the "thousand years" (not a literal 1000 years) spoken of in Revelation 20.