A comment on confusion about the story of Sa‘d ibn al-Rabi‘ divorcing his wife so that ‘Abd al-Rahman ibn ‘Awf could marry her
Question

I've learned that Islam teaches spouses to love one another and be attached to one another after Nikah and stay with each other with tranquility.
But I have some confusions about a Hadith (Bukhari 3781) in which the Noble Sahaba Sa`d bin Ar-Rabi` offers to let go of many of his blessings so as to give them to Abdur Rahman bin Awf (May Allah be pleased with them both) including divorcing one of his wife's so that bin Awf could marry her after her iddah.
My confusions are :
1) although the intention of bin Ar Rabi is very selfless, is it not unfair that his wife, who loves him much, would be made to separate with her husband, for no fault of hers, and be married off to a new man, possibly causing her great pain and turmoil because of the separation?
2) how is possible that a man can tell his wife to marry someone else after he divorces her? And is it the teaching of Islam, to divorce one's beloved wife by telling her that he is divorcing her because she should marry another man? Is this a legitimate reason?
3)If bin Ar Rabi did divorce one of his wives, and she refused to marry bin Ar Awf, then wouldn't it cause more damage than good?
4) in the Hadith, bin Ar Rabi tells bin Ar Rawf that he could chose from any of his two wives.
Does Islam allow a non Mahram male to look at and chose from women who are already married?
Praise be to Allah.Firstly:
The great selflessness of the Ansar
Al-Bukhari (3781) narrated from Anas (may Allah be pleased with him) that he said: ‘Abd al-Rahman ibn ‘Awf came to us, and the Messenger of Allah (blessings and peace of Allah be upon him) instituted the bond of brotherhood between him and Sa‘d ibn al-Rabi‘, who was very wealthy. Sa‘d said: The Ansar know that I am one of the wealthiest of them, so I will divide my wealth equally between me and you. And I have two wives, so see which of them you like better, and I will divorce her so that when she becomes lawful, you may marry her. ‘Abd al-Rahman said: May Allah bless your family for you. [He went to the market to trade] and did not return on that day until he had acquired some gain of ghee and dried yoghurt. [He went on trading] until, within a short time, he came to the Messenger of Allah (blessings and peace of Allah be upon him) with traces of yellow perfume on him. The Messenger of Allah (blessings and peace of Allah be upon him) said to him: “What is this scent?” He said: I have married a woman of the Ansar. He said: “What mahr did you give her?” He said: A date-stone’s weight of gold, or a date-stone of gold. He said: “Give a wedding feast (walimah), even with one sheep.”
This is an example of the greatest selflessness, in which a man gives precedence to his brother over himself in that regard. He did not stop at offering to give up one of his wives for him; rather he give him the option of choosing the better one, for he was married to two women, as it was narrated by Ahmad (13863) that Sa‘d said: I have two wives, so see which of them you like best, so that I may divorce her…
Hence Allah praised the Ansar by saying (interpretation of the meaning):
{And those who were already settled in the land [of Madinah] before them, and were sincere in faith, love the Muhajirun who came to them, and find no covetous desire in their hearts for what they have been given. Rather they give them preference over themselves, even if they too are poor. Those who are protected from their own covetousness – it is they who will be the successful ones} [al-Hashr 59:9].
This selflessness is not something that was found exclusively among the men of the Ansar; rather their women were the same. Undoubtedly Sa‘d ibn al-Rabi‘ (may Allah be pleased with him) knew from the attitude and faith of his wives that they would not object to this selflessness, and would never let him down, and that one of them would leave her husband and marry someone else to fulfil his wish and share with him in the reward and being brought close to Allah.
So we should not compare their situation to ours and how stingy we are, for they were far above what we could imagine.
Moreover, the Arabs did not see anything wrong with that, meaning that a man would divorce his wife, then she would marry someone else. The matter of marriage and divorce was something easy for them.
Secondly:
Divorce for no reason and no need is disliked (makruh), and it was said that it is prohibited (haram), but this was a case of great need, which was the need to help the Muhajirin who had been expelled from their land and lost their wealth.
Thirdly:
A comment on the action of the Sahabi mentioned in this report
Choosing the wife which he liked best was not something that was limited only to looking at the woman. There are many other factors to be considered when choosing a wife, such as her lineage, her age and whether she has children or not. Moreover, hijab had not yet been enjoined, so it was possible to see her, and it was also possible to find out about her from other women.
What matters is that this did not happen, so there is no need to make assumptions about the way in which the choice was made. Rather what happened is what is recorded in the reports. This is the unique selflessness that Allah instilled in the supporters of His cause and the supporters (Ansar) of His Messenger Muhammad (blessings and peace of Allah be upon him).
There is no need to imagine or assume anything. It is sufficient for us to know that Allah praised these people (the Ansar) and is pleased with them, and that they gave precedence to their brothers over themselves, and their brothers, the Muhajirin, responded by thanking them and refraining from taking them up on such offers.
What the Sahabi suggested did not happen at all, so why do we need to ask this question or to suggest that if that had happened, it would have been something bad or unfair, or to describe it as such and such, when it did not even happen?
Rather we should focus on the point of this story, which is the great selflessness of the companions of the Prophet (blessings and peace of Allah be upon him), their love of good for their brothers, and their being free of stinginess even with regard to that which was most precious to them, namely their wives, so how about other matters?
May Allah be pleased with them all, and may He make us among those of whom He says (interpretation of the meaning):
{And [there is a share for] those who came after them, saying, “Our Lord, forgive us and our brothers who preceded us in faith and put not in our hearts [any] resentment toward those who have believed. Our Lord, indeed You are Kind and Merciful”} [al-Hashr 59:10].
And Allah knows best.