Short answer
Because the Prophet ﷺ kissed it, not because the stone has power. Umar ibn al-Khattab said he knew it was a stone that could neither harm nor benefit and kissed it only because he saw the Prophet do so. Kissing or touching it at the start of each round of tawaf is sunnah if you can do it without harming anyone; otherwise you point to it.
Istilam (touching and kissing) of the Black Stone at the start and in each round of tawaf is sunnah. Pushing or hurting people to reach it is not allowed, since harm is haram and the sunnah is fulfilled by pointing with the palms and saying the takbir.
The four schools agree on this.
Explanation
The Black Stone (al-Hajar al-Aswad) is set in the eastern corner of the Kaaba and marks the start of each round of tawaf. The Prophet ﷺ said it came down from Paradise whiter than milk and was blackened by the sins of the children of Adam. Muslims honour it as one of the symbols of Allah, while believing that only Allah benefits or harms.
- Best: place your hands on it, kiss it gently and say Bismillah, Allahu akbar.
- Crowded: touch it with your hand and kiss your hand.
- Cannot reach: face it, raise your palms toward it, say Bismillah, Allahu akbar, and walk on. The Prophet himself pointed at it during a tawaf on his camel.
- In ihram: the stone is often perfumed, so avoid touching it if perfume would stick to you.
- Women: should not push into crowds of men to reach it; pointing is enough.
- The Yemeni corner: touch it with the hand if you can, but do not kiss it or point to it.
The four schools agree on the main points, with small differences over how to greet the Yemeni corner. For whether Muslims worship the Kaaba, see do Muslims worship the Kaaba, and for its history, Kaaba facts.
The evidence
Quran, Surah Al-Hajj 22:32
ذَٰلِكَ وَمَن يُعَظِّمْ شَعَٰٓئِرَ ٱللَّهِ فَإِنَّهَا مِن تَقْوَى ٱلْقُلُوبِ ﴿٣٢﴾
That [is so]. And whoever honors the symbols of Allah - indeed, it is from the piety of hearts.
Honouring Allah's symbols comes from taqwa.
Sahih al-Bukhari 1597
Sahih... إني أعلم أنك حجر لا تضر ولا تنفع ولولا أني رأيت النبي صلى الله عليه وسلم يقبلك ما قبلتك ...
"I know you are a stone that neither harms nor benefits; had I not seen the Prophet kiss you, I would not have kissed you."
The stone is kissed only to follow the Sunnah.
Sahih al-Bukhari 1613
Sahih... طاف النبي صلى الله عليه وسلم بالبيت على بعير كلما أتى الركن أشار إليه ...
"The Prophet did tawaf of the House on a camel; every time he came to the corner he pointed at it and said the takbir."
Pointing is enough when touching is not possible.
Jami' at-Tirmidhi 877
Grading to be checked... نزل الحجر الأسود من الجنة وهو أشد بياضا من اللبن ...
"The Black Stone came down from Paradise whiter than milk, and the sins of the children of Adam blackened it."
The stone's origin and honour.
Where the ruling is recorded
- al-Hidaya, Kitab al-Hajj, on tawaf, istilam of the Black Stone. Kiss it if possible without harming anyone; otherwise touch it or point to it.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Hajj, on istilam. Harming people to reach it is not permitted.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.