Most non-Muslims do not understand the concept Ibadah (worship) in Islam. Some times they worship Jesus or gods and still claim they worship One God and at times they are unable to differentiate between kissing, revering and worshipping. Ibadah is from the word Abd in Arabic. Abd means bondsman. So Ibadah is bondage. We bow in worship, ask guidance from, pray to Him alone whose we are bondsmen. No Muslim in the world asks guidance from or prays to Hajar-e-Aswad (the Black Stone in Kaabah). We do not ascribe any power of giving life, death or sustenance to Hajar-e-Aswad. It can neither directly nor indirectly help or harm us in any way. We hold the Quran with revere and kiss it but we do not worship it. Many non-Muslims insist on calling it worship of the stone to justify their idol worship or worship of other creations of God. Some of them insist that Muslims worship Kaabah as they prostrate in that direction and yes, some even declare that Muslims worship the mosques! You can’t help it if even after explaining that Kaabah has no power to help or harm us, they ascribe Kaabah worship to you. Muslims do not worship Hajar-e-Aswad, it is plain enough. But why do they kiss it? Why did the Prophet (Pbuh) kiss it? That is a different question.
Hajar-e-Aswad is not an ordinary stone. It was brought from heavens by the Archangel Jibriel to be affixed in a corner of the wall of Kaabah. The traditions say that it was like a shining gem when it was brought but the sins of the children of Adam caused it to blacken. There are inferences from some traditions and some of the words of the prayers said at Kaabah that it has the records of all the human beings affirmation of Allah’s Lordship in the nether world before the man was sent to earth. When a person kisses it or raises a hand to it in affirmation, his actual deeds are tallied with his original covenant recorded in it and his sins and deviations from his covenant are imprinted on it in the form of blackness. How? We do not know. May be after some time when the science is more advanced, we will be able to understand the record of all the human beings as we understand huge records in a small zip drive today.
To those who may call it a myth or fairy tail, Hazrat Umar, the second Caliph had provided a simple answer. He once said before the Hajar-e-Aswad: Thou hast no power. Thou art a stone, a creation. I kiss thou only because the Prophet (Pbuh) had kissed you.