COMMENTARY on 4:129
Mustafa Khattab:

Translation:
You will never be able to maintain ˹emotional˺ justice between your wives—no matter how keen you are. So do not totally incline towards one leaving the other in suspense.39 And if you do what is right and are mindful ˹of Allah˺, surely Allah is All-Forgiving, Most Merciful.
Commentary:
39   Do not leave one hanging—not fully enjoying the rights of a married woman and not fully divorced.

 

A. Yusuf Ali:

Translation:
You are never able to be fair and just as between women, even if it is your ardent desire: But turn not away (from a woman) altogether, so as to leave her (as it were) hanging (in the air). 639 If you come to a friendly understanding, and practise self- restraint, Allah is Oft-forgiving, Most Merciful.
Commentary:

639  In this material world there are two principal causes of division between man and wife, money and "the other woman" or "the other man". Money was dealt with in the last verse. Here is the case of "the other woman". Legally more than one wife (up to four) are permissible on the condition that the man can be perfectly fair and just to all. But this is a condition almost impossible to fulfil. If, in the hope that he might be able to fulfil it, a man puts himself in that impossible position, it is only right to insist that he should not discard one but at least fulfil all the outward duties that are incumbent on him in respect of her.

 

Muhammad Asad:

Translation:
And it will not be within your power to treat your wives with equal fairness, however much you may desire it; 147 and so, do not allow yourselves to incline towards one to the exclusion of the other, leaving her in a state, as it were, of having and not having a husband. 148 But if you put things to rights and are conscious of Him - behold, God is indeed much-forgiving, a dispenser of grace.
Commentary:
147  This refers to cases where a man has more than one wife - a permission which is conditional upon his determination and ability to "treat them with equal fairness", as laid down in verse 3 of this surah. Since a man who is fully conscious of his moral responsibility might feel that he is committing a sin if he loves one of his wives more than the other (or others), the above verse provides a "judicial enlightenment" on this point by making it clear that feelings are beyond a human being's control: in other words, that the required equality of treatment relates only to outward behaviour towards and practical dealings with one's wives. However, in view of the fact that a man's behaviour towards another person is, in the long run, almost inevitably influenced by what he feels about that person, the above passage - read in conjunction with verse 3, and especially its concluding sentence - imposes a moral restriction on plural marriages.
148  Lit., "do not incline with all inclination" - i.e., towards one of the wives, implying thereby an exclusion of the other from all affection - "leaving her, as it were, in suspense (kal-mu allaqah)''. Regarding my rendering of this phrase, see Lane V, 2137.