Praise be to Allah.
“What is meant by the words of the Prophet (blessings and peace of Allah be upon him), “Hajj is ‘Arafah” is that in Hajj it is essential to stand in ‘Arafah . Whoever does not stand in ‘Arafah has missed out on Hajj .
It does not mean that the one who stands in ‘Arafah no longer has to do any of the actions of Hajj, according to scholarly consensus, because if a person stands in ‘Arafah, he still has to do some actions of Hajj , such as staying overnight in Muzdalifah, tawaf al-ifadah, sa‘i between as-Safa and al-Marwah, stoning the Jamarat and staying overnight in Mina.
Rather, what is meant is that standing in ‘Arafah is an essential part of Hajj and if he does not stand in ‘Arafah, then there is no Hajj for him. Hence the scholars said: Whoever misses the standing (in ‘Arafah) has missed Hajj.” (Majmu` Fatawa Ibn Uthaymin, 23/24)
And Allah knows best.