يَوْمَ لَا يَنفَعُ مَالٌ وَلَا بَنُونَ ۝ إِلَّا مَن أَتَى اللَّهَ بِقَلْبٍ سَلِيمٍ

These verses deal with right understanding, i.e. seeing things as they really are. For a subject of God, this is the greatest blessing next to prophethood. That is why it is mentioned in a tradition which says, ‘If God wants to do something good to a man, He bestows on him the understanding of religion.’ Whatever Abraham asked for in his prayer was granted to him, but the prayer for the pardon of his father (Azar) was rejected. One can imagine from this that prayer (du‘a) is mostly a matter between God and His subject. One man’s prayer cannot obtain pardon for another man. Before Almighty God, real value attaches to a pure heart (qalb salim). This means the right kind of pure heart, i.e. a heart which is free from the tendency to ascribe partners to God, feelings of hypocrisy, jealousy and ill-will. In other words, the believer should go before God with a heart as pure as it was at the time of his birth. He should not present himself before God with any other heart.

— Source: Tazkirul Quran (Maulana Wahiduddin Khan) via Quran.com (26:88)