Sufyan al-Thawri said: “Your past sins” means what you did during the pre-Islamic period, and “your future sins” means everything you have not done. Such an expression is used for emphasis, as when one says, “He gave to whoever saw him and whoever did not see him,” or, “He struck whoever met him and whoever did not meet him.”
Ata al-Khurasani said: “Your past sin” means the sin of your parents, Adam and Eve, through your blessing; and “your future sins” means the sins of your community through your supplication. (1)
“And complete His favor upon you” through Prophethood and wisdom; “and guide you to a straight path,” that is, make you steadfast upon it. The meaning is that, together with the conquest, the completion of favor through forgiveness and guidance to the straight path—which is Islam—may be combined for you. It was also said that “guide you” means: guide others through you.
“And that Allah may help you with a mighty victory (3). It is He who sent down tranquility into the hearts of the believers, so that they may add faith to their faith. To Allah belong the forces of the heavens and the earth, and Allah is All-Knowing, All-Wise (4).”
“And that Allah may help you with a mighty victory”: a prevailing victory. It was also said: one that confers honor.
“It is He who sent down tranquility”—serenity and dignity—“into the hearts of the believers,” so that their souls would not be disturbed by what befalls them. Ibn Abbas said: Every instance of tranquility in the Quran means serenity, except that which occurs in Surah al-Baqarah: “so that they may add faith to their faith.”
Ibn Abbas said: Allah sent His Messenger with the testimony that there is no god but Allah. When they believed him, He added the prayer for them, then zakah, then fasting, then pilgrimage, then jihad, until He perfected their religion for them. (2) Thus, whenever they were commanded to do something and affirmed it, their affirmation increased upon their previous affirmation.
Al-Dahhak said: Certainty added to their certainty.
Al-Kalbi said: This concerns the matter of Hudaybiyyah, when Allah fulfilled His Messenger’s vision in truth.
“To Allah belong the forces of the heavens and the earth, and Allah is All-Knowing, All-Wise.”