He says,

لِيُبَيِّنَ لَهُمُ ...

In order that He may make clear to them,

means, to mankind,

... الَّذِي يَخْتَلِفُونَ فِيهِ ...

what they differed over,

means, every dispute.

لِيَجْزِىَ الَّذِينَ أَسَاءُواْ بِمَا عَمِلُواْ وَيِجْزِى الَّذِينَ أَحْسَنُواْ بِالْحُسْنَى

that He may requite those who do evil with that which they have done (i.e. punish them in Hell), and reward those who do good, with what is best (i.e. Paradise). (53:31)

... وَلِيَعْلَمَ الَّذِينَ كَفَرُواْ أَنَّهُمْ كَانُواْ كَاذِبِينَ ﴿٣٩﴾

and so that those who disbelieved may know that they were liars.

meaning that they lied in their oaths and their swearing that Allah would not resurrect those who die. Thus they will be pushed down by force to the Fire with horrible force on the Day of Resurrection, and the guards of Hell will say to them:

هَـذِهِ النَّارُ الَّتِى كُنتُم بِهَا تُكَذِّبُونَ

أَفَسِحْرٌ هَـذَا أَمْ أَنتُمْ لاَ تُبْصِرُونَ

اصْلَوْهَا فَاصْبِرُواْ أَوْ لاَ تَصْبِرُواْ سَوَآءٌ عَلَيْكُمْ إِنَّمَا تُجْزَوْنَ مَا كُنتُمْ تَعْمَلُونَ

This is the Fire which you used to belie. Is this magic or do you not see Taste its heat, and whether you are tolerant of it or intolerant of it - it is all the same. You are only being requited for what you have done. (52:14-16)

Then Allah tells us about His ability to do whatever He wills, and that nothing is impossible for Him on earth or in heaven. When He wants a thing, all He has to do is say to it "Be!'' and it is.

The Resurrection is one such thing, when He wants it to happen, all He will have to do is issue the command once, and it will happen as He wills, as He says:

وَمَآ أَمْرُنَآ إِلاَّ وَحِدَةٌ كَلَمْحٍ بِالْبَصَرِ

And Our commandment is but one as the twinkling of an eye. (54:50)

and,

مَّا خَلْقُكُمْ وَلاَ بَعْثُكُمْ إِلاَّ كَنَفْسٍ وَحِدَةٍ

The creation of you all and the resurrection of you all are only as (the creation and resurrection of) a single person. (31:28)

And in this Ayah, Allah says: