When a part is mentioned in the Shari'ah to mean the whole, and examples of this

The Shaykh : It is like the verse of prayer, what is it? Fajr This is an Arabic style where a part is mentioned to mean the whole, in order to indicate the importance of the part. It is like his saying (peace and blessings be upon him): I wonder if a person went and did nothing but stand at 'Arafah, he has not performed Hajj, but what does the Messenger say? "Hajj is 'Arafah." He mentioned the part and meant what? The whole. Why did he mention the part? Because of its importance. Therefore, the scholars agreed that standing at 'Arafah is a pillar of Hajj, so whoever does not stand at 'Arafah, his Hajj is invalid.