It is they who are the fools, because they exchanged faith for disbelief; and this exchange did not help them in any way, because they lost their faith in Allah and lost the way to the truth.
These are they who have purchased error with guidance, so their commerce was profitless. And they were not guided (16)
In his Tafsir, As-Suddi reported that Ibn 'Abbas and Ibn Mas'ud commented on;
أُولَٰئِكَ الَّذِينَ اشْتَرَوُا الضَّلَالَةَ بِالْهُدَىٰ
(These are they who have purchased error with guidance) saying it means, "They pursued misguidance and abandoned guidance. " Mujahid said, "They believed and then disbelieved," while Qatadah said, "They preferred deviation to guidance." Qatadah's statement is similar in meaning to Allah's statement about Thamud,
وَأَمَّا ثَمُودُ فَهَدَيْنَاهُمْ فَاسْتَحَبُّوا الْعَمَىٰ عَلَى الْهُدَىٰ
(And as for Thamud, We granted them guidance, but they preferred blindness to guidance)(41:17).
In summary, the statements that we have mentioned from the scholars of Tafsir indicate that the hypocrites deviate from the true guidance and prefer misguidance, substituting wickedness in place of righteousness. This meaning explains Allah's statement,
أُولَٰئِكَ الَّذِينَ اشْتَرَوُا الضَّلَالَةَ بِالْهُدَىٰ
(These are they who have purchased error with guidance), meaning, they exchanged guidance to buy misguidance. This meaning includes those who first believed, then later disbelieved, whom Allah described,
ذَٰلِكَ بِأَنَّهُمْ آمَنُوا ثُمَّ كَفَرُوا فَطُبِعَ عَلَىٰ قُلُوبِهِمْ
(That is because they believed, and then disbelieved; therefore their hearts are sealed)(63:3).
The Ayah also includes those who preferred deviation over guidance. The hypocrites fall into several categories. This is why Allah said,
فَمَا رَبِحَت تِّجَارَتُهُمْ وَمَا كَانُوا مُهْتَدِينَ
(So their commerce was profitless. And they were not guided), meaning their trade did not succeed nor were they righteous or rightly guided throughout all this. In addition, Ibn Jarir narrated that Qatadah commented on the Ayah,
فَمَا رَبِحَت تِّجَارَتُهُمْ وَمَا كَانُوا مُهْتَدِينَ
(So their commerce was profitless. And they were not guided), "By Allah! I have seen them leaving guidance for deviation, leaving the Jama'ah (the community of the believers) for the sects, leaving safety for fear, and the Sunnah for innovation." Ibn Abi Hatim also reported other similar statements.
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.
In a dark room black and white look the same, but as soon as the lights are turned on, black appears as black, and white as white. The same is true of the message of God, which was revealed to the prophets. The divine scriptures are God’s beacons to the world. When this light is shed upon mankind, guidance and error clearly appear for what they are. It becomes evident what good and evil deeds consist of, and what their consequences are. But some people, instead of bowing to the truth, want the truth to be subservient to them. The light of God only serves to confuse them. Their hidden jealousy and pride take hold of them. As soon as they see themselves in the divine mirror, their negative sentiments are aroused. Deep-rooted prejudices overcome their senses. They have eyes, but cannot see; they have ears, but cannot hear; they have tongues, but cannot speak. They can neither hear the call of truth, nor respond to it in any way, nor can they find their way by any sign from God. Instead of reflecting upon the call of truth, as they should do, they evade it either by attaching no importance to it, or by not listening to it at all.