Jesus said it: ".....because, looking, they look in vain, and hearing they hear in vain, neither do they get the sense of it; and toward them the prophecy of Isaiah is having fulfillment, which says, 'By hearing, you will hear but by no means get the sense of it; and, looking, you will look but by no means see." Matthew 13.13,14
They appear to try. Look at John 5.39: "You are searching the scriptures, because you think by means of them you will have everlasting life and these are the very ones that bear witness about me."
Paul put it this way in 2Thess.2.9-12 " But the lawless one’s presence is by the operation of Satan+ with every powerful work and lying signs and wonders*+ 10 and every unrighteous deception+ for those who are perishing, as a retribution because they did not accept the love of the truth in order that they might be saved. 11 That is why God lets a deluding influence mislead them so that they may come to believe the lie,+ 12 in order that they all may be judged because they did not believe the truth but took pleasure in unrighteousness."
Romans 3.14:" But their mental powers were dulled."
One such one that has escaped Trinitarianism a Professor who taught at Masters University and ended up resigning because of the doctrine wrote:
"Trinitarians are victims of a kind of a kind of cult-ish persuasion, where once someone has been thoroughly indoctrinated into a system of theology, they are unable to read Scripture and ascertain it's true historical meaning, but are bound to see in it's pages, only the theology into which they were indoctrinated.
It's like in Romans 11.8 Paul speaks of these ones: just as it is written: “God has given them a spirit of deep sleep,+ eyes that do not see and ears that do not hear, down to this very day.
