al-Istitaʿa is explained in two ways:
1. al-Istitaʿa is used in the sense of having financial means or capability; in the following verses, it carries this meaning:
"If we had istitāʿa {that is, financial means!}, we would certainly have gone out with you" {that is, we would have joined you in the expedition to Tabuk!} they will swear to Allah... Allah knows that they are surely liars {that is, He knows they actually had the financial means to join the expedition}. (al-Tawba 9:42)
And [due] to Allah from the people is a right of pilgrimage to the House [Kaʿba] for whoever is istitāʿa to the way {that is, whoever has the financial means to reach the Kaʿba}. (Āl ʿImrān 3:97)
And whoever among you does not have istitāʿa to marry free, believing women {that is, does not have the necessary financial means for this}... (al-Nisāʾ 4:25)
Except for those who are istitāʿa {that is, do not have the financial means to leave Mecca and migrate to Medina} and cannot find [a way]... (al-Nisāʾ 4:98)
2. al-Istitaʿa is used in the sense of strength or ability; as in the following verses:
You will never be able to istitāʿa justice {that is, you will not have the strength} between women [in affection]. (al-Nisāʾ 4:129) They are not able to istitāʿa hearing {that is, they do not have the strength to hear iman (faith), they are not capable of it}. (Hūd 11:20)
They were not able to istitāʿa standing [against punishment] {that is, they did not find the strength to withstand the punishment}. (al-Dhāriyāt 51:45)
So have taqwa (God-consciousness) of Allah as much as your istitāʿa {that is, as much as your strength allows}. (al-Taghābun 64:16)
Indeed, they have denied what you say, so you cannot istitāʿa [to avert] nor [find] help {that is, you have no strength and are not capable of it}. (al-Furqān 25:19)