Al-e-Imran (The House of Imran) Sura 3: Verse 216
"But those who disbelieve after having believed, and then increase in their unbelief - their repentance shall not be accepted. They are the ones utterly astray. As to those who disbelieve, and die while they are disbelievers, there shall not be accepted from any of them even the earth full of gold, though they should offer it in ransom. For them, there shall be a painful punishment, and they shall have no helpers."
These verses refer to the people whose repentance shall not be accepted. They are the ones who were guilty of all the above-mentioned crimes: they believed and then went back and disbelieved, and then went on adding layers upon layers of disbelief. When their final moment came, they professed repentance verbally, without making amends for their crimes, nor openly confessing their concealment of the truth before the Prophet and the believers. Also, they did not spend in the cause of Allah and in support of the Prophet in order to wipe off their sins. They died, in the words of the Quran, falsely hoping that "Allah shall forgive us - sa-yughfiru lana". The Quran clearly warns all such people who thus delude themselves that their verbal repentance is no real repentance, nor will Allah accept it from them.
Similar is the case of those people who recognised the truth and believed in it and then reverted to kufr or unbelief and died in this state. Such people, even if they were to offer the earth full of gold in ransom to save themselves from the chastisement, it shall not be accepted from them. The style used here is meant to emphasise the impossibility of their salvation in the hereafter, for surely no one will possess anything in the hereafter to be able to offer it to anyone else, nor is the life hereafter a place for wheeling and dealing. The conclusion - Wa ma la-hum min nasirin - and they shall have no helpers - lays bare the false hopes of those who expected to be saved by the intercession of their forefathers on their behalf.
"Pondering Over The Qur'an: Surah Ali Imran" - Amin Ahsan Islahi