Why is Haji pilgrimage important for Muslims?
Qur'an says it is obligatory for all Muslims who are physically able and can afford it (Surah 3:97)
Hajj is seen as a powerful demonstration of the unity of the ummah, with Muslims from different denominations and countries converging in one place for the purpose of worship/fulfilling requirement of faith.
It means Muslims can see the Kaaba - the House of God - for themselves, strengthening their faith and relationship with God. This has long-lasting effects.
It is an opportunity for sins to be forgiven.