A.W. Pink in that article of his that I posted maintained that men in Adam have no spiritual ability because they don't want to understand, learn, seek after God, repent, believe, etc. It's just not in their spiritual DNA. Here's a passage I came across in Proverbs that essentially teaches this truth in a pithy way that only a godly word of wisdom could:
Prov 29:19
19 A servant cannot be corrected by mere words;
though he understands, he will not respond.
NIV
In other words, it's because "he will not respond" that he cannot be corrected by mere words. But even more than this: It's because he will not respond, it can also be said that he doesn't truly understand. He understands with his head -- but not with his heart. Head knowledge is one thing; heart knowledge, however, is very different because when all the faculties are engaged the whole man is affected. And this truth accounts for why so much is written about man's heart in scripture.