“They will recite the Qur’an but it will not pass beyond their throats”
This doesn’t mean that they will have no imaan in their hearts, but they will lack knowledge, and this lack of knowledge will move them into actions that will cause them to go out of the religion just as the arrow passes through an animal.
They will, in other words, be proficient in reading and reciting, but they will not possess understanding of what they read. They will not have the ability to contextualize ayaat against other ayaat, against the evidences from the Sunnah, against the explanations of the ayaat by the Sahabah and early scholars. They will take ayaat according to their own understanding of them, which is almost always simplistic, and this will cause them to fall into great error.
I know about this, because I used to do it when I first came to Islam. I had studied enough to know. I wanted to enter Islam, but I had not studied enough to know how to remain in Islam. This is why you see many converts being drawn to the Jihadi movements…they have zeal and imaan, without sufficient knowledge. They fall into the same mistakes that keep recurring among extremist groups throughout our history. But, al-Hamdulillah, the remedy is available and accessible…knowledge is attainable, and the sources of knowledge are not monopolized by a secretive clergy. Everyone can read Ibn Kathir, everyone can read as-Suyooti, everyone can read Fath al Bari…etc…particularly if Arabic is your native tongue.