These are they who have purchased error for guidance, so their commerce was profitless. And they were not guided. (2:16)

Allah is certifying those losers, who wasted all of their efforts towards matters related to this world. Now how can one buy misguidance against guidance simply those who wasted most of their time against the will of Allah, by not obeying his laws, meaning that person has followed Satan, because there is no other way. Either the way of Allah and his Prophet, or the way of Satan. Any efforts towards this world which does not involve the laws of Islam, this means that person is obeying Satan, this is how that person has purchased misguidance instead of guidance.

All business, places, trading, cars, status, wealth nothing will help regardless what we build in this world, without the involvements of Islamic law. So these are those who have been misguided, and they will never be amongst those who are guided. It is never to late, if we open our eyes after understanding the verses from the Qur'an, then the doors of repentance are never closed.

Note: However the doors of repentance are never closed until death, and we should cry and beg to Allah in order to open our eyes and hearing so we can understand the orders of our creator, sustainer, and our provider, we should always remember that Allah's mercy is more stronger then his punishments, if one tries to seek it within his lifetime, inshallah.