I do not know why Islam does not allow the man to marry his wife again if he has divorced her then he wants to take her back. The Qur’an states that she has to marry another man first, then only after that can the first husband marry her again. That does not seem logical to me; rather I think it is harsh.
What the individual must do is obey the commands of Allah, may He be exalted, and be certain that He is the most wise of judges; His command cannot be rejected and His rule cannot be overturned. There is wisdom and goodness in all His rulings, and they are in our best interests.
“And who is better in judgement than Allah for a people who have firm Faith?”
Because He, may He be glorified, is the Creator of His slaves, He knows best what is in their interests. He, may He be glorified, has no need of His slaves, is far above any injustice, and is most merciful to His creation. As He is like that, His rulings must be the ultimate in justice, wisdom and compassion.
The individual may know the wisdom behind the commands and prohibitions, or he may be unaware of it, but he is enjoined to obey in all circumstances, because this is the state of the weak slave before the Almighty Lord and Sovereign. If he disputes the wisdom of his Creator (in a particular ruling), he has gone beyond the bounds of faith and true servitude to Allah, as He, may He be exalted, says (interpretation of the meaning):
“It is not for a believer, man or woman, when Allah and His Messenger have decreed a matter that they should have any option in their decision. And whoever disobeys Allah and His Messenger, he has indeed strayed in a plain error”
“But no, by your Lord, they can have no Faith, until they make you (O Muhammad SAW) judge in all disputes between them, and find in themselves no resistance against your decisions, and accept (them) with full submission”
There is nothing to prevent the individual from asking and looking for the wisdom behind rulings, in order to increase his faith and certainty.
The one who ponders the issue of divorce will become certain of the mercy and wisdom of Allah. Divorce is painful and harmful for the woman, hence the Lawgiver is very strict about it and has restricted it so that people will not be heedless about it.
If the man, every time he divorced his wife, was able to make a new marriage contract with her and take her back, a man might divorce his wife dozens of times, and each time he would be harming her and breaking her heart, then people of goodwill would try to reconcile between them, or the woman might feel sorry for her children, so she goes back to her husband. This is obviously unfair and unjust to her.
But if the husband knows that the third divorce will make his wife irrevocably divorced from him, in the sense that he will not be able to take her back until after she has married another man who then dies or divorces her, but he may not die or divorce her, then he would be afraid of divorce and would keep away from it, and he would not resort to it except in cases of necessity or urgent need. In that there is mercy for the wife and protection for the family, and it prevents people being heedless about the matter or toying with it.
There is also another kind of wisdom behind it, which is that the man may be hasty in divorcing the first time, then he may regret it and take his wife back. Then if he divorces her a second time, he will be doing so with insight and knowledge. Then if he divorces her a third time, that – in most cases – will indicate that they cannot live a stable life together, so there is no point in carrying on with this miserable life, and perhaps separation will be a relief and mercy for both of them, as Allah, may He be exalted, says (interpretation of the meaning):
“But if they separate (by divorce), Allah will provide abundance for everyone of them from His Bounty. And Allah is Ever All-Sufficient for His creatures need, All-Wise”
The scholars have commented on the wisdom behind making divorce three times:
At-Taahir ibn ‘Aashoor (may Allah have mercy on him) said:
The wisdom behind this great legislation is to deter husbands from taking their wives’ rights lightly and making them like toys in their houses. So the husband is given the first divorce as a mistake, the second as a test and the third as a separation, as the Messenger of Allah (blessings and peace of Allah be upon him) said in the hadeeth about Moosa and al-Khidr: “The first time was due to forgetfulness on the part of Moosa, the second time led to the stipulation of a condition, and the third time was deliberate. Hence al-Khidr said to him after the third time: ‘This is the parting between me and you’ [al-Kahf 18:78].”
End quote from at-Tahreer wa’t-Tanweer, 5/415
Ibn al-Humaam al-Hanafi (may Allah have mercy on him) said: He may have false feelings that he does not need her (his wife) any more, or that there is a need to leave her, then this idea may take hold of the individual, but when the divorce takes place, he may regret it and feel distressed and become impatient (to take her back). Therefore Allah, may He be glorified and exalted, ordained that divorce may be done three times, so that he might test himself the first time. Then if the reality of divorce confirms his feelings, he may persist until the ‘iddah ends. Otherwise he can try to redeem the situation by taking her back, then if he again feels as he did the first time and that feeling becomes so overwhelming that he divorces her again, he will have another opportunity to think about it after the second divorce. Then by the time he issues the third divorce, he will be very certain of what he wants to do, and after the third divorce there are no more excuses.
End quote from Sharh Fath al-Qadeer, 3/465
And Allah knows best.