O mankind! There has certainly come to you an advice (mawʿiẓa) from your Lord, and a cure for what is in the breasts (ṣudūr), and a guidance (hudan) and mercy (raḥma) for the faithful.
If we consider the four attributes that God has ascribed to the Qurʾan in the this verse—namely, that it is an admonition, a cure for what is in the breasts, a guidance, and a mercy—and compare these to one other, then this verse serves as a comprehensive exposition of the Qurʾan’s beautiful, wholesome effects and the pure, untainted knowledge that is instilled in the souls of the believers from the moment it reaches their ears until it takes root in their souls and settles in their hearts.
The Qurʾan first reaches the believers while they are enveloped by heedlessness and beset by confusion, which have caused their inner selves to be filled with the darkness of doubt and skepticism, and their hearts to be afflicted with the diseases of vices and all sorts of wicked and despicable states. This being their condition, the Qurʾan delivers a beautiful admonition to them that awakens them from the slumber of heedlessness, dissuades them from their evil habits and bad deeds, and directs them instead towards goodness and happiness.
After this, it sets about purifying their inner selves from the impurities of vices and negative moral attributes, and it continues to remove the afflictions of their minds and cure the diseases of their hearts one after another until they are all gone.
After this, it gently guides them to true knowledge, noble morals, and righteous deeds, elevating them step by step and drawing them closer to the ranks of the ones brought near to God (al-muqarrabūn), until they finally settle among them and achieve the success reserved for those who are sincerely devoted to Him.
Finally, it clothes them in the garments of mercy, settles them in the abode of honor, and grants them the joy of being in the company of prophets, truthful ones, witnesses, and the righteous—an excellent company indeed. It admits them into the ranks of God’s closest servants who are lodged in the highest of the heavens.
Ref: a, English Volume 19 (Tawheed Institute Australia)