مَّا خَلْقُكُمْ وَلاَ بَعْثُكُمْ إِلاَّا كَنَفْسٍ وَاحِدَةٍ
...
The creation of you all and the resurrection of you all are only as a single person.
means, His creation and resurrection of all of mankind on the Day of Resurrection is, in relation to His power, like the creation and resurrection of a single soul; all of this is easy for Him.
إِنَّمَأ أَمْرُهُ إِذَا أَرَادَ شَيْياً أَن يَقُولَ لَهُ كُن فَيَكُونُ
Verily, His command, when He intends a thing, is only that He says to it, "Be!" -- and it is! (36:82)
وَمَأ أَمْرُنَأ إِلاَّ وَحِدَةٌ كَلَمْحٍ بِالْبَصَرِ
And Our commandment is but one as the twinkling of an eye. (54:50)
This means He only has to command a thing once, and it will happen. There is no need for Him to repeat it or confirm it.
فَإِنَّمَا هِىَ زَجْرَةٌ وَحِدَةٌ
فَإِذَا هُم بِالسَّاهِرَةِ
But it will be only a single Zajrah. When behold, they find themselves on the surface of the earth alive after their death. (79:13-14)
...
إِنَّ اللَّهَ سَمِيعٌ بَصِيرٌ
Verily, Allah is All-Hearer, All-Seer.
means, just as He hears all that they say, so He also sees all that they do, as if He is hearing and seeing a single soul. His power over all of them is like His power over a single soul, Allah says:
مَّا خَلْقُكُمْ وَلاَ بَعْثُكُمْ إِلاَّا كَنَفْسٍ وَاحِدَةٍ
(The creation of you all and the resurrection of you all are only as a single person).