[22].Surah Al-Hajj [The Pilgrimage]: Ayat 26

Ayat 26. And (remember) when We showed Ibrahim (PBUH)(Abraham) the site of the (Sacred) House (the Kabah at Makkah) (saying): "Associate not anything (in worship) with Me, [Lâ ilaha ill-Allah (none has the right to be worshipped but Allah Islamic Monotheism], and sanctify My House for those who circumambulate it, and those who stand up for prayer, and those who bow (submit themselves with humility and obedience to Allah), and make prostration (in prayer, etc.);"

[Tafseer] Behold! We gave the site, to Abraham PBUH, of the (Sacred) House, (saying): "Associate not anything (in worship) with Me; and sanctify My House for those who compass it round, or stand up, or bow, or prostrate themselves (therein in prayer). The site of Makkah was granted to Abraham PBHU (and his son Ismail PBUH) for a place of worship that was to be pure {without idols, the worship being paid to Allah, the One True God) and universal, without being reserved (like Solomon's Temple of later times) to any one People or Race. Note that here the word qa'imin (who stand up for prayer) occurs in place of 'akifin (who use it as a retreat). In practice the meaning is the same. Those who go for a retreat to the Kabah stay there for the time being. 

Hazrat Abu Hurairah (May Allah be pleased with him) reported: The Messenger of Allah [SAWW](PBUH) said, "(The performance of) `Umrah is an expiation for the sins committed between it and the previous `Umrah; and the reward of Hajj Mabrur (i.e., one accepted) is nothing but Jannah.'' 

[Al-Bukhari Book 03, Chapter 27, Hadith # 01] 

Lesson : as mentioned above in Surah Al-Hajj Ayat 26."sanctify My House for those who circumambulate it" This Hadith tells us that the merit of Umrah is that it is an expiation for sins. But this, too, is an expiation for minor sins. `Umrah includes assuming Ihram, circumambulation of Kabah, going between As-Safa and Al-Marwah and Halq or Taqsir (shaving of head or cutting hair).