Walan tastateeAAoo an taAAdiloo bayna annisa-i walaw harastum fala tameeloo kulla almayli (surah Nisa: 129)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(4:129) You will not be able to treat your wives with absolute justice not even when you keenly desire to do so. (It suffices in order to follow the Law of Allah that) you incline not wholly to one, leaving the other in suspense. *161 If you act rightly and remain God-fearing, surely Allah is All-Forgiving, All-Compassionate. *162

Wa lan tastatee`ooo an ta`diloo bainan nisaaa`i wa law harastum falaa tameeloo kullal maili fatazaroohaa kalmu`al laqah; wa in tuslihoo wa tattaqoo fa innal laaha kaana Ghafoorar Raheema

*161). This means that it is not possible for a man to accord complete equality of treatment to two or more wives under all circumstances and in all respects. It is possible that one is ugly, the other beautiful; one is old, the other young; one is permanently sick, the other healthy; one is irritable, the other good-tempered. These and other differences are likely to make a person less attracted to one and more to the other. In such circumstances, the Law does not demand that one should necessarily maintain absolute equality between the wives in respect of love, emotional attachment and sexual relationship. What it does demand is that if a husband does not repudiate the marriage despite aversion for his wife, either because of his own desire or out of consideration for the desire of his wife, he should at least maintain a good relationship short of which his wife begins to feel as if she is without a husband. In such circumstances, while it is natural that a person should prefer one wife to the other, this should not go to the extent that the woman remains, as it were, in a state of suspension, as if she were without a husband at all.
Some people point out that in this verse the Qur'an in one breath stipulates justice as the necessary condition for plurality of wives and in the other breath declares it to be impossible. On this ground they conclude that the Qur'an has itself revoked the permission to marry more than one wife. There is, however, absolutely no justification for such an inference. Such an inference would have been justified had the Qur'an merely said that 'You will not be able to treat your wives with (absolute) justice.' But this statement has been followed by the directive: ' ... do not allow yourselves to incline wholly to one, leaving the other in suspense.' This leaves no grounds at all for the blind followers of Christian Europe to force an interpretation of their liking on the verse.
*162). If a man does not deliberately inflict any wrong and tries earnestly to be just in his dealings God will pardon whatever minor shortcomings take place.