Quranic commentary with no reference to the seerah would be dull. Such a commentary would be like a body without its soul. At the same time, Quran provides information alluding to a certain event, or an argument to a particular dispute, or a sentiment felt or affected by a certain personality involved, or the sociological, psychological and political conditions at a given time.
For that reason, Quran is an indispensable source for seerah. At the same time, seerah enlightens Quranic commentary. One complements and completes the other.
Let's briefly review one surah in the Quran to illustrate the above points.
For the purpose of brevity, Surah Al-Masadd (no. 111) is selected. Its translation is given here:
Damned the two hands of Abu Lahab, and damned he! [1] Neither his wealth availed him, nor what he earned. [2] He will soon enter a fire, full of flames, [3] and his wife as well, the wicked carrier of firewood. [4] In her neck there is a rope of twisted palm-fibre. [5] (Translation by Muhammad Shameem, Mohammad Wali Raazi and Muhammad Taqi Usmani, with the original word perish replaced with damned)
Now, anyone without any knowledge whatsoever about the seerah would be at a loss as to what the surah Al-Masadd is all about. The interpretation of that surah could not be ventured unless one knows about the story and the actors involved behind it. This is the case whereby the knowledge on seerah is indispensable for Quranic commentary.
But if one is well acquainted with the seerah, then he would know that this surah is directed to Abu Lahab, the uncle of the Prophet, whose real name is Abdul Uzza bin Abdul Muttalib, but was called Abu Lahab, the Father of the Flames, on account of the radiant look on his face, which look like a flame.
He was the staunchest enemy of the Prophet from the same clan. Other clan members who did not believe in the Prophet were willing to protect him on account of clan loyalty, but Abu Lahab broke his link with his clan and joined other polytheists fighting against the Prophet and the members of his own clan. He was among the richest in the Banu Hashim clan, the clan of the Prophet.
He was married to Arwa bint Harb bin Umayyah, the sister of Abu Sufyan bin Harb, another archenemy of the Prophet. Known as Umm Jamil, she was among the women who caused the most trouble to the Prophet, both in her words and her actions. As for her words, she was fond of lampooning and making fun of Muhammad.
She was a beautiful woman (which is probably why she is called Umm Jamil) and had a knack for poetry, which she composed to lampoon the Prophet. As for the actions, she was fond of throwing thorns, firewood, feces, rubbish, etc in front of the Prophet's house and along his path. And sometimes on the Prophet's body as well. Abu Lahab and his wife were the Prophet's neighbor.
With that background, one can start seeing the picture forming in the surah. The allusion to the actors, their behavior, their status, their wealth, their feelings, sentiments, attitudes, etc., starts to make sense. From thereon, the commentator can proceed to the meaning and implication of the surah, or commenting on the beauty and harmony of the verses, such as the connection between the person Abu Lahab, who will be burned in the lahab (burning flames).
Similar connection may be seen about his wife's penchant for throwing thorns, firewood and rubbish to the Prophet, and the wicked woman carrying firewood with the rope on her neck.
This surah was revealed after the Prophet gathered the Qurasyh nearby Kaabah to proclaim Islam publicly, which took place after the third year of his prophethood. Right after the Prophet finished addressing his audience, Abu Lahab, in a fit of anger, shouted, "tabbak," which means damned you, doomed you, or perish you. His full sentence was: "Damned you! For this have you called us?"
Immediately after that, this surah was revealed using the same word used by Abu Lahab. The only different is that instead of "tabbak," meaning damned you, the words used are "tabbat yada," which means damned the two hands. The two hands refer to Abu Lahab's power and his actions, which, along with his wealth and children, will be of no use to him in the Hereafter. For what he had done with his power, wealth and children, Abu Lahab will be burned in the burning flames, the lahab.
With that background weaves together, it adds spice to the beauty and harmony of the surah, as well as heightens the significance of its message, namely, one reaps what one toils. The bad deeds and cruelties directed by these couple to the Prophet will redound back to them in the Hereafter.
Such is the significance of seerah to Quranic interpretation. As for the Quran providing information to the seerah, in one short sweep, this surah highlights the moods, sentiments, and the reactions of the Prophet's enemies against him and his message.