Surah Ash-Sharh (94) — Ayah 1

(Ayah 1){ اَلَمْ نَشْرَحْ لَكَ صَدْرَكَ:} By opening the breast is meant contentment upon the truth of Islam, the heart being illuminated with the light of guidance, and being softened by the remembrance of Allah, as Allah the Exalted has said: «فَمَنْ يُّرِدِ اللّٰهُ اَنْ يَّهْدِيَهٗ يَشْرَحْ صَدْرَهٗ لِلْاِسْلَامِ » [الأنعام : ۱۲۵ ] "So whomever Allah intends to guide, He opens his breast to Islam." And He said: « اَفَمَنْ شَرَحَ اللّٰهُ صَدْرَهٗ لِلْاِسْلَامِ فَهُوَ عَلٰى نُوْرٍ مِّنْ رَّبِّهٖ فَوَيْلٌ لِّلْقٰسِيَةِ قُلُوْبُهُمْ مِّنْ ذِكْرِ اللّٰهِ اُولٰٓىِٕكَ فِيْ ضَلٰلٍ مُّبِيْنٍ » [ الزمر : ۲۲ ] "So is the one whose breast Allah has opened to Islam, so he is upon a light from his Lord (can he be like the one who is not)? Then woe to those whose hearts are hardened against the remembrance of Allah; they are in clear error." Besides this, by the opening of the breast is also meant the temperament being willingly prepared to bear the responsibilities of prophethood, as when Musa (peace be upon him) was commanded to go to Pharaoh, he said: «وَ يَضِيْقُ صَدْرِيْ » [ الشعراء : ۱۳ ] "And my breast is constricted because of that." And he prayed: «رَبِّ اشْرَحْ لِيْ صَدْرِيْ » [ طٰہٰ : ۲۵ ] "O my Lord! Open my breast for me."
Included in the opening of the breast is also the filling of your (Prophet Muhammad's ﷺ) breast with faith and wisdom after the splitting of your chest , which occurred in childhood, at the beginning of the revelation, and on the night of Mi'raj, as has come in the Sahihayn and other books of hadith.

1. Did We not expand for you your chest (1)

Did We not expand your chest for you [1]?

[1]
Two Meanings of Sharh Sadr:

The word "Sharh Sadr" is used in two senses. One is that a person fully understands a matter, ideology, belief, or issue. There remains no doubt, suspicion, or ambiguity, and the person attains certainty and satisfaction regarding what he has understood, as it is said: ﴿فَمَنْ يُّرِدِ اللّٰهُ اَنْ يَّهدِيَهٗ يَشْرَحْ صَدْرَهٗ لِلْاِسْلَامِ﴾ [126:2] "That is, whomever Allah intends to guide, He opens his chest for Islam," meaning he attains the certainty and satisfaction that the beliefs presented by Islam are indeed correct. The second meaning of this word is that when a person considers a task to be very difficult and feels burdened to accomplish it, his nature becomes willing to undertake and bear this burden, as when Allah Almighty granted prophethood to Sayyiduna Musa ؑ and commanded him to go to Pharaoh and deliver His message. At that time, he prayed: ﴿قَالَ رَبِّ اشْرَحْ لِيْ صَدْرِيْ﴾ [20:25۔26] "That is, O my Lord, open my chest for me and make this (difficult) task easy for me." In this verse, an interrogative style has been adopted, which sheds light on its background. The fact is that when you ﷺ began the work of inviting to Islam, the very people who used to sing your praises and you were the beloved of the entire nation, became your enemies. This was both painful and astonishing for you ﷺ, but in these circumstances, Allah Almighty granted such great courage to the Prophet of Islam and the Muslims who embraced Islam that, despite enduring the persecutions of the disbelievers of Makkah, they neither bowed before them nor were subdued. And above all, the greatest courage was granted to you ﷺ, because the main target of the disbelievers was your blessed person. Mocking you ﷺ, your prophethood, the verses of Allah, and your words was the favorite pastime of the disbelievers, and what could be a greater extent of physical torment than the fact that, during the Makkan period, the disbelievers made seven assassination attempts on you. (For details, see the footnote of Surah Al-Ma'idah, verse 67.) In addition, whenever any Muslim was subjected to oppression and persecution, you equally shared in that pain. In this verse, Allah Almighty has reminded of this favor: Have We not granted you courage as strong as a rock to endure these hardships? For further details, refer to my book "Muhammad ﷺ... The Embodiment of Patience and Steadfastness."