And give the women (on marriage) their dower as a free gift; but if they, of their own good pleasure, remit any part of it to you, Take it and enjoy it with right good cheer.
In pre-Islamic times, when a man wanted to marry a woman, he would pay a “sale” price to her father or other responsible male relative. Islam changed that custom and instead made the woman the owner of her own freedom and the one who receives her dowry, which would be like an insurance policy for her against future loss, divorce or an opportunity for her to invest to augment her own livelihood. Thus, when a Muslim man desires to marry any woman, he has to gain her consent and then pay the dowry directly to her at the time of the marriage ceremony. (The word for dowry in Arabic is mahr, but in this verse it is referred to as sadaqa, a word that implies a gift given in honest friendship. See 2:236.) The woman can set the dowry as she likes, and it belongs exclusively to her. If a woman sets a very high dowry and her groom is unable to pay it all, she may defer its payment at a later date. If a man passes away before the payment of the dowry is completed, then its value must come out of his estate and be paid to his widow as a debt owed to her. (In modern times, there has been a curious trend, encouraged by men for obvious reasons, in which women are encouraged to take ‘the high road’ and ask for only token dowries. There is no shame in Islam, however, for asking for substantial dowries, and many women coupled with such men have later regretted their paltry compensation.)
This verse counsels men to pay the dowry in a spirit of good cheer, and not grudgingly, which is a kind of unfair pressure on their wife-to-be. A man is not allowed to take back any dowry he gave his wife after he marries her. If the wife later remits some of it of her own free-will, then take it as a double boon. The Prophet said, “Beware! Do not wrong. Remember that a person’s property is not lawful (for you to take) unless he gives it to you of his own free will.” (Mishkat)
Emerick, Yahiya. The Meaning of the Holy Qur’an in Today’s English (p. 829). Unknown. Kindle Edition.