What are the essential pillars of Hajj without which Hajj is not valid? [The Manner of Hajj]

The Shaykh : The first question: What are the essential pillars of Hajj without which Hajj is not valid?
Ihram: Ihram for Hajj is like the intention for prayer; it is the intention of prayer, which is that you say, "Labbaik Allahumma bi-hajjatin wa 'umrah" (Here I am, O Allah, for Hajj and 'Umrah). We do not want to go into the details now so as not to stray from the scope of answering the questions, but it is necessary to point out that the intention for Hajj today must begin with the intention of 'Umrah before the Hajj. So you say, "Labbaik Allahumma bi-'umrah" (Here I am, O Allah, for 'Umrah), and you do not say, "Labbaik Allahumma bi-hajjatin" (Here I am, O Allah, for Hajj) or "bi-hajj" (for Hajj), because it is necessary to precede the Hajj with the 'Umrah. This is because the Messenger (peace and blessings be upon him) said and he interlaced his fingers, and this means that the 'Umrah has become an inseparable part of the Hajj. So the one who wants to perform Hajj today begins with the 'Umrah. Therefore, the first condition is the intention, but the intention for Hajj, regarding the Tamattu' type where we say it is necessary to begin with 'Umrah, is made while you are in Makkah. However, if you leave your country and pass through one of the known Miqat boundaries, then the Miqat for us, the people of the Levant, is from Dhul-Hulayfah, and there you enter the state of Ihram for the 'Umrah of Hajj. And while you are in Makkah, you enter the state of Ihram for Hajj on the eighth day of Dhul-Hijjah, saying, "Labbaik Allahumma bi-hajjatin" (Here I am, O Allah, for Hajj). At the Miqat, you say, "Labbaik Allahumma bi-'umrah" (Here I am, O Allah, for 'Umrah), and while you are in Makkah, where you are staying, you say, "Labbaik Allahumma bi-hajjatin" (Here I am, O Allah, for Hajj). Then comes the Tawaf around the Ka'bah, then standing at 'Arafah. These are the pillars that are necessary, plus staying overnight at Muzdalifah, where you pray the Fajr prayer, and this is a pillar according to the most correct of the scholars' opinions, and the Tawaf al-Ifadah. These are the pillars of Hajj that are necessary, and everything else is obligations, or if you wish, duties, and the meaning is the same.