What is the meaning of the Prophet's saying, "Hajj is Arafah"?

The meaning of "Hajj is Arafah" is that standing at Arafah is a fundamental pillar; whoever misses standing there has missed the Hajj. It does not mean that merely by standing at Arafah the Hajj concludes. Rather, the pilgrim still has other rituals to perform, such as spending the night in Muzdalifah, performing the circumambulation of Ifadah (Tawaf al-Ifadah), the striving (Sa'i), the throwing of pebbles (ramy), and spending the night in Mina.