Allah tells us of His might, pride, majesty, beautiful Names and sublime attributes , and His perfect Words which no one can encompass. No human being knows their essence or nature, or how many they are. Allah says ”And if all the trees on the earth were pens and the sea, with seven seas behind it to add to it, yet the Words of Allah would not be exhausted.” meaning, even if all the trees on earth were made into pens and the sea was made into ink, and topped up with seven more like it, and they were used to write the Words of Allah showing His might, attributes and majesty, the pens would break and the ink would run dry, even if more were brought.
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.