[3:90] Surely those who disbelieve after they have believed, and then increase in unbelief, their repentance shall not be accepted; those are the ones who go astray.
The allusion in it is that those who return to the states of the people of habit after having traveled the way of desire (?arīq al-irāda). They preferred this world and following caprice (hawāÌ) over seeking the Real (swt), so they renounced the people of the path and became more and more lonely in their darknesses. Their repentance shall not be accepted; those are the ones who go astray [3:90] from the path of the Real and their faith shall not be accepted after the appearance of faithlessness. Their punishment is that, as the days pass, the estrangement of the heart from the path only increases for them, and they are not distressed by the clarity of state which has slipped away from them. If they had persevered, their repentance would have been accepted, but the Real (s) follows His way (sunna) with those who are listless on this path when they revert to habitual states (aḥwāl al-ʿāda), not feeling regret for the moments that have passed away from them. God Most High said: And We shall confound their hearts and eyes; just as they did not believe in it the first time [6:110]. The apostate from Islam is a more powerful enemy to Muslims than the regular disbeliever. Likewise, the one who reverts from this path is more powerful in rejecting it and more oppositional to its people than those who were always alien to it.