What is Hajj? Linguistically Hajj means to intend something, go somewhere. In this particular case you are intending to visit the Kabah, the House of Allah.
The mosque is definitely a place of spiritual purification and spiritual renewal. When we go to Makkah, we must understand that one prayer in this mosque is equivalent to 100,000 prayers.
When we go there to worship Allah, to circumambulate around it and carry out the other rituals of Hajj, we understand why Hajj is the 5th pillar of Islam.