Here Allah commands His Messenger to convey the Message and recite the Qur'an to people. He tells him that he will be brought back to the return, which is the Day of Resurrection, where he will be asked about the prophethood he was entrusted with. So Allah says:

meaning, the One Who has commanded you to put it into practice among mankind,'

'On the Day of Resurrection, where He will question you concerning that,' as Allah said:

{Then surely, We shall question those to whom it was sent and verily, We shall question the Messengers.} (7:6)

Allah said:

{On the Day when Allah will gather the Messengers together and say to them: "What was the response you received?"} (5:109).

And He said:

{and the Prophets and the witnesses will be brought forward} (39:69)

In his Tafsir of his Sahih, Al-Bukhari recorded that Ibn 'Abbas commented on the Ayah:

“To Makkah.” This was also recorded by An-Nasa'i in his Tafsir in his Sunan, and by Ibn Jarir. Al-'Awfi also reported from Ibn 'Abbas that the phrase:

means, “will surely bring you back to Makkah as He brought you out of it.” Muhammad bin Ishaq recorded that Mujahid commented on:

He said, “Back to your place of birth in Makkah.”

Ibn 'Abbas is also reported to have interpreted it variously referring to death, to the Day of Resurrection which will come after death, and to Paradise which will be his reward and his destiny for putting the Message of Allah into practice and conveying it to the humans and Jinns, and because he is the most perfect, most eloquent and most noble of all the creation of Allah.

Allah's saying:

means: “Say, O Muhammad, to those among your people who oppose you and disbelieve you, among the idolators and those who follow them in their disbelief, 'My Lord knows best which of us, you or I, is rightly guided, and you will come to know for which of us will be the (happy) end in the Hereafter, and for which of us will be a good end and victory in this world and in the Hereafter'.” Then Allah reminds His Prophet the numerous blessings He granted to him and mankind by virtue of sending him to them:

'Before the revelation was sent down to you, you did not expect that revelation would be sent down to you.'

means, but revelation has been sent down to you from Allah as a mercy to you and to mankind because of you. Since Allah has granted you this great blessing,'

{So never be a supporter} i.e., a helper,

{of the disbelievers.} rather, separate from them, 'express your hostility towards them and oppose them.'

meaning, 'Do not let their opposition to you affect you or put people off from following your way; do not worry about that or pay any attention to it, for Allah will make your word supreme, will support your religion and will make the Message with which He has sent you prevail over all other religions.' So He says:

{and invite to your Lord} to worship your Lord Alone, with no partners or associates,

means, it is not appropriate to worship anything or anybody except Him, and divinity does not befit any except His glory.

{Everything will perish save His Face'}. Here Allah is telling us that He is Eternal, Ever Lasting, Ever Living, Self-Sustaining, Who, although His creation dies, He will never die, as He says:

{Whatsoever is on it will perish. And the Face of your Lord full of majesty and honor will remain forever.} (55:26-27).

Allah used the word “Face” to refer to Himself, as He says here:

meaning, everything except Him. It was reported in the Sahih. via Abu Salamah that Abu Hurayrah said, “The Messenger of Allah said:

«The truest word of a poet was the saying of Labid - indeed everything except Allah is false.»

{His is the decision} means, dominion and control, and there is none who can reverse His judgement or decision.

means, on the Day when you will be brought back, and He will reward or punish you according to your deeds: if they are good, then you will be rewarded, and if they are bad, then you will be punished.

This is the end of the Tafsir of Surat Al-Qasas. To Allah be praise and blessings.