Imam has undertaken very useful discussions in this regard in his precious book of “ an exposition on Forth Hadith”. He explains as following:
For about forty years you imagine that you have been performing virtuous deeds in order to please God, whereas it occurs in a hadith that whosoever remains faithful to God for forty days, springs of wisdom emanate from his heart.
This is, therefore, a sign for us to comprehend that our deeds were not performed for the sake of God, though we ourselves are not conscious of it, and this is the main cause of our irremediable sickness.
Imam further explains that pitiable is the condition of the devotees, worshippers, leaders and followers of Friday congregations and men of high knowledge and learning! When they will open their eyes in the court of the Most High on the Day of Judgment, they will come to know that they are not only among the sinners, perpetrators of major sins, but even worse than infidels and idolaters, and their record of deeds even darker than theirs.
It is a matter of pity for a person that his prayers and other devotional acts should serve as fuel for the fires of hell. May God save us from the moment when, in spite of one’s alms-giving and zakat and piety, one’s appearance will be distorted to such hideousness that it is not even imaginable.
You, a helpless creature, are branded as a mushrik, an idolater, and a sinner despite your belief in the Unity of God.
God willing, He will forgive the sinners by His mercy, but for the mushrik He has said that He will not forgive him if he dies without repentance.
Read more:
Human Nature from Viewpoint of Imam Khomeini