After the rapture, during the ensuing Tribulation period, there will be absolutely no hidden Christians and no hidden atheists. All will be forced to declare one way or another. (Rev 13:16). Meanwhile at the present time, we see more and more hared of Jesus on earth.
"it is not what goes into the mouth that defiles a person, but what comes out of the mouth; this defiles a person." Matthew 15:11
Matthew Henry: "Christ shows that the defilement they ought to fear, was not from what entered their mouths as food, but from what came out of their mouths, which showed the wickedness of their hearts."
Nowadays to me, it feels like a parallel to the prophesied time as the Millennial Kingdom is about to come to a close. After the 7-year Tribulation ends, there is a period of 1000 years when Jesus physically rules on earth. (Revelation 20:4). This is known as the millennial kingdom when all the promises Jesus made to His people Israel are fulfilled spiritually and physically with the full lands being given to them and His personal attendance in a renewed Temple (Ezekiel 41). At the end of the 1000 years of Jesus' kingdom rule on earth, where sin had been subdued and satan had been locked up, but where there still have been mortals born, satan will be let out of his abyss jail and he will deceive the nations. It takes satan but a moment to draw the wicked to himself, immediately exposing the wickedness in their hearts that had been there all along. (Revelation 20:7-9). It feels like that now, with satan accelerating his evil doings to draw more and more people to himself. The cup of heart-poison overflows in many and shows in their words and deeds.
The great shifting of peoples hearts is the movement toward Jesus or away from Jesus. When the rapture occurs, the believers from the beginning at the time from the beginning of the church age (Jesus' ascension) the very rapturous trumpet call will be resurrected or those who are alive will be lifted up and all will meet in the air to be with Jesus. Those remaining on earth will be those who chose not to believe. There will still be time for some of them to come to faith afterward, but the Church Age ends at the rapture with the last believer filling God's quota of His church coming to faith. (Romans 11:25).
Then the 1000-year Kingdom, then the new heaven and earth, and the eternal state with the final Judgment of all humans.
At the end the gulf between those who believe and those who do not will be exposed and settled at the Great White Throne Judgment. (Revelation 20:11-15) when all who have ever lived will give an account and receive their final body and their punishment will begin.
Wicked hearts are surely being shown today in great numbers. The venom that is in them is spilling out of mouths that deliberately or unknowingly proclaim for satan. We see it in their hatred of Kim Davis, the Kentucky clerk who refused to issue homosexual marriage licenses. We see it in their hypocrisy against Christian football player Tim Tebow but worldly acceptance and lauding of Bruce Jenner's depraved gender switch. We see it in the new Deist/Atheist Declaration of Sinlessness, blasphemies against Jesus, mob anger, violence. All this is in the heart, and is now coming out in torrents. They are storing up their sin for themselves.
Yet...there is One heart that is pure and undefiled, that is Jesus.
"For our heart rejoices in Him, Because we trust in His holy name." (Psalms 33:21)
Bless His holy name, He is coming soon.