In the Name of Allah, The Most Gracious, Most Merciful
Since the Hajj act of worship was ordained by Allah on those who are capable once in a lifetime, if a pilgrim violates its rites and fails to perform one of its requirements or if he neglects a sunnah,if he sticks to a sunnah that has led to the violation of something prohibited, or if he commits an act of disobedience, if he performs a prohibited action, his pilgrimage would be null and void or he may have to sacrifice an animal. If he does wrong, if he neglects to do something that he has to do, if he fails to perform what is a priority - if he does that he would waste a unique opportunity that is not repeated, an opportunity to have his sin forgiven and to qualify him to be admitted to Allah's paradise. All this is due to ignorance, which is the utmost enemy of man. An ignorant person may harm himself beyond what his enemy may harm him. Therefore, we say: dear pilgrims learn the provisions of pilgrimage before you go on Hajj. Thus ,one knowledgeable person is more difficult for Satan to seduce than a thousand worshippers, and a little knowledge of the principles of worship is better than a lot of worship:
﴾So ask of those who know the Scripture if you know not. ﴿And just as awaiting the time of prayer is considered part of the prayer, similarly preparing oneself for Hajj is part of the Hajj. Many pilgrims have failed to learn the necessary Hajj provisions before going on pilgrimage and they returned from Hajj without having performed the basic tawaf (circumambulation) with the result that their pilgrimage would be null and void. Many a pilgrim has crossed the miqat (local point of ihram; official commencement of the duties of Hajj) without having put on the Ihram garments with the result that he needed to sacrifice an animal. And how many a pilgrim has violated the rules of Ihram thinking that he was on the right track..