وَوَجَدَكَ عَآئِلًا فَأَغْنَىٰ
Root: ع-ي-ل. Poverty, straitness of livelihood. ʿĀla yaʿīlu — he fell into poverty, his means grew narrow.
The same root in the Qurʾān: "And if you fear poverty…" (al-Tawba 9/28).
There is a neighbouring root, and the two must not be confused: the root ع-و-ل. ʿĀla yaʿūlu — to be under obligation to maintain, to provide for. The words ʿāʾila (family) and ʿiyāl (those a person supports) come from this field. The same root is also discussed in the Qurʾān in the sense "to deviate from justice": "That is more likely that you will not do injustice" (al-Nisāʾ 4/3) — the meaning of the verb taʿūlū here is disputed among the exegetes.
The lexicographers keep these two roots apart. But that their fields of meaning should be neighbours is no coincidence: there is a direct relation between a household to be provided for and straitness of livelihood.
Why not "faqīran"? For poverty the Qurʾān generally uses the word فقير (faqīr). The concrete sense of the root faqr has to do with the breaking of the spine, or with the vertebra (faqār) — that is, the bending of the back, becoming unable to carry.
Here ʿāʾil is chosen. The difference is fine and not suited to a definite ruling; but ʿāʾil stands closer to "one who struggles to make his living come out even" than to "one who has no property". The verse-ending may also have played a part.
Root: غ-ن-ي. It is usually rendered in English as "wealth", but the original sense of the root is freedom from need. Istighnāʾ means not standing in need of a thing.
Al-Ghanī is one of the names of God and carries exactly this sense: "O people! You are the ones in need of God; and God is al-Ghanī, al-Ḥamīd" (Fāṭir 35/15). This connection was made when the word al-Ṣamad was treated in Sūrat al-Ikhlāṣ: the one who is not in need, the one who is needed.
The root has a second use as well, and it occurs often in the Qurʾān: aghnā ʿan — "to ward something off from someone, to be of avail to him". "His wealth and what he earned did not avail him" (al-Masad 111/2); "My wealth has not availed me" (al-Ḥāqqa 69/28). That is, ghinā is not the amount of what is in hand but the usefulness of what is in hand.
According to the historical sources, the Prophet's material situation changed through his marriage to Khadīja and through trade. But care is needed here: the Prophet was never among the wealthy of Mecca, and he spent the greater part of his life plainly. Many of the reports transmitted about the Medinan period describe that no fire was lit in his house for long stretches and that he kept to a plain living.
Reading aghnā solely as an accumulation of property therefore puts the verse into conflict with history.
A second reading resolves this difficulty: ghinā al-nafs — contentment of heart, the one who wants coming to want no longer. This reading is supported by a ḥadīth: that the Prophet said "Wealth is not an abundance of goods; true wealth is the wealth of the soul" is transmitted from Abū Hurayra in al-Bukhārī and Muslim.
And this reading is confirmed within the sūra itself. The fifth verse had said "you will be content". Riḍā and ghinā look to the same place: both are measured not by amount but by the state of the one who wants.
The root's sense of "freedom from need" already contains this. A person becomes free of need in one of two ways: either what he has in hand increases, or his wanting decreases. The word is wide enough to cover both, and the verse does not narrow it.