The number seven is used to indicate a large amount, it is not to be taken literally or to be understood as referring to the seven oceans of the world.
”Verily, Allah is All-Mighty, All-Wise” means He is All-Mighty and has subjugated all things to His will, so nothing can prevent what He wills, and none can oppose or put back His decision. He is All-Wise in His creation, commands, Words, actions, Laws and all His affairs.
”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.
”Verily Allah is All-Hearer, All-Seer” means just as He hears all that they say, so He also sees all they do, as if He is hearing and seeing a single soul. His power over all of them is like His power over one single soul.
Culled from Tafsir bn Kathir.
