What is meant when we are taught that we should not be averse to polygamy?

It is perfectly natural for a wife to feel averse to her husband marrying a second wife. The Promised Messiah ^as wrote:

It is God who is One and without any associate. However, women do not at all like to have an associate either. A saint says that one of his neighbors was very harsh with his wife. One day he decided to marry a second wife. On this, his wife was deeply saddened and said to her husband, “I bore all of the pain you gave me, but I will not tolerate this pain, that you being my husband will make another my associate.” The saint said that this statement of her’s left a very painful impression on his heart, and he wished to find a similar statement in the Holy Quran. On this, he found the following verse:

Allah will not forgive that any partner be associated with Him; but He will forgive whatever is short of that to whomsoever He pleases (Surah an-Nisa’, 4:49).

On the surface, this is a very delicate affair. It is observed that just as the indignation of a man does not wish that his woman be shared between him and someone else, similarly the indignation of a woman does not desire that her man be shared between her and someone other than her. However I know for certain that there is no defect in the teaching of God Almighty, nor is it contrary to the characteristics of human nature. The full reality is that the indignation of man is a true and complete indignation, the removal of which is actually beyond cure. However, the indignation of women is not complete, rather, it is completely doubtful and it declines. What the Holy Prophet ^sas said to Hadrat Umme Salama ^ra gives great insight. Hadrat Umme Salama ^ra responded to the proposal of the Holy Prophet ^sas by saying that she was a woman with great indignation, and since he ^sas had many wives and may marry more in the future, so she may not be able to bear to see other wives. On this, the Holy Prophet ^sas said that I will pray for you that God Almighty remove your indignation and grant you patience.

(Tafsir Hadrat Masih Mau‘ud, vol. 3, p. 213–214)

We are only taught that we should not be averse to the teaching of polygamy. The Promised Messiah ^as said:

There is also in women a bad habit, that when the husband of a woman wishes to marry a second time for some expedience of his, the woman and her relatives become very angry and use profanity and create an uproar, and unjustly harass this good man. Such women and their relatives are useless and unrighteous. Allah Almighty has, in His perfect wisdom in which there are hundreds of expediences, permitted men that they, at the time of any needs or expediences of theirs, can marry up to four wives. Then, when someone marries according to the command of Allah and His Prophet, why should it be called bad. Such women and their relatives with these habits, who oppose God and His prophet’s commands, are very rejected and are sisters and brothers of satan. Turning away from the word of Allah and the Prophet ^sas, they seek to fight their Lord. If any good-natured Muslim has such a wicked wife in his home, then it is appropriate that he definitely marry a second time to punish her.

(Tafsir Hadrat Masih Mau‘ud, vol. 3, p. 213)

Here, the Promised Messiah ^as is speaking of wives who oppose the very teaching of polygamy, and he is speaking of husbands who are righteous and marry according to the teachings of Islam.

If a wife is not averse to the teaching of polygamy, there is nothing wrong with her being personally averse to her husband marrying a second wife. For example, if a person is getting married for the first time, but we do not think he is ready for marriage, we have every right to be displeased with the marriage. However, if we believe a marriage is wrong because the concept of celibacy is right and the concept of marriage is wrong, then our displeasure would be against Islam. Similarly, if a man is getting married a second time, but we do not think he is ready for a second marriage, we have every right to be displeased with the marriage. But if we believe a second marriage is wrong because the concept of polygamy is wrong, then our displeasure would be against Islam. The Promised Messiah ^as wrote:

If the first wife feels that her rights as a wife will be placed in jeopardy by the second marriage of her husband, she can seek a way out of the situation by demanding a divorce; and should the husband be unwilling to comply with her demand, she can enforce separation through the court.

(Essence of Islam, vol. 3, p. 318–319)

The Promised Messiah ^as also said:

If a husband desires, for some genuine reason, and under Divine law, to avail this permission, and his wife is not happy about it, she has the options to demand divorce, and be rid of this anxiety. And if the other woman, whom he wishes to marry, is not happy, she too has the easy option to decline the offer of such a suitor. No one is under compulsion.

(Essence of Islam, vol. 3, p. 318)