﴿ أُو۟لَٰٓئِكَ ٱلَّذِينَ ٱشْتَرَوُا۟ ٱلضَّلَٰلَةَ بِٱلْهُدَىٰ فَمَا رَبِحَت تِّجَٰرَتُهُمْ وَمَا كَانُوا۟ مُهْتَدِينَ ﴾

“[for] it is they who have taken error in exchange for guidance; and neither has their bargain brought them gain, nor have they found guidance [elsewhere].”

The ninth verse shows the basic denseness of the hypocrites - how they failed to make use of the ordinary sense of discrimination. They had grown up in a pagan society, and knew very well what the way of the infidels was. Now they had become familiar enough with Islam too, and could easily see the difference. But, in their greed, and for the sake of petty worldly profit, they still chose disbelief as against Islam, and bartered away something as invaluable as Iman ایمان (faith) for something as worthless, and even harmful as kufr کفر (infidelity). In giving the name of 'trade' or 'commerce' to this action, the Holy Qur'an suggests that these worldly-wise men had no understanding even of the art of trading.