“To create all of you or to resurrect all of you is to Him like (creating or resurrecting) a single person. Verily Allah is All-Hearing, All-Seeing.” (Al Qur’an – 31:28)
God is Omnipotent. He is All-Hearing and All-Seeing. He hears all voices and all sounds quite distinctly at once and at the same time, of course without any exhaustion and distraction. He does so in such a way that none of the sounds or voices makes Him oblivious of others. In like manner, He simultaneously observes the entire universe and all objects and events in it in the minutest detail. Yet the observation of these objects does not absorb Him totally so as to prevent Him from observing other objects and events. All this is of course quite Divine. A human being can deviate from his chosen path, and get involved in digration from his observation and concentration. But God is God; He can do multiple of acts simultaneously and that too without any digration and without any feeling of thirst, hunger, perspiration or exhaustion, or for that matter any other thing like that.
The same holds true about His causing the birth of human beings and raising them to life after they die. God has the power to resurrect all those who were ever born, right from the beginning of human life until the Last Day. His creating some does not prevent Him from simultaneously creating others. For Him, it is all the same whether He creates a single person or billions of them.