Assalaamu alaykum Brother. I was just wondering why God will judge all of us at the same time when everyone is dead. Why does He not send us to heaven or hell and judge us as soon as we die instead of doing everyone on the Day of Judgement, if you know what I mean? May Allaah reward you.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

The duty of the believer is to submit to the wisdom of Allaah and refrain from objecting to His actions and commands; Allaah, The Exalted, says (what means): {He is not questioned about what He does, but they will be questioned.} [Quran 21:23]

The Hanafi scholar Ibn Abi Al-ʻIzz wrote in his commentary on Al-ʻAqeedah At-Tahaawiyyah, “You should know that the cornerstone of servitude to Allaah and belief in Him, His Books, and His Messengers is total submission and refraining from asking questions about the details of the wisdom behind His commands, prohibitions, and legislation...”

There is no doubt that Allaah, The Exalted, is All-Wise; behind each Order of Allaah is a great wisdom that might be known to some people but unknown to others. Our ignorance of that wisdom does not mean that there is no a wisdom behind it; it rather means that we come short of knowing the wisdom of Allaah. He says (what means): {Allaah knows what is (presently) before them and what will be after them, but they do not encompass it in knowledge.} [Quran 20:110]

However, Allaah may impart some knowledge of the wisdom behind His actions to whomever He chooses of His slaves.

We have noticed that you have sent several questions in the same vein. We advise you to beware of the evil consequences of raising undue questions about the divine wisdom behind the actions of Allaah, for this may undermine your faith.

That said, there is no doubt that there is great wisdom behind the reckoning of all of mankind on the Day of Judgment before their Lord, such as celebrating His great might in gathering all of mankind in one place and taking them all to account together. It also celebrates His generosity towards the believers and the disgrace and humiliation of the disbelievers and sinners  before the whole creation. In addition, prolonged waiting for the reckoning and enduring the accompanied hardships are aspects of the punishment of Allaah for the sinners and enemies of Allaah, and at the same time they are trials that cancel out some of the sins of the believers. These are but mere examples of the possible wisdom behind the reckoning of all of mankind on the Day of Judgment.

Allaah knows best.