Quran 30:21:

And of His signs is that He created for you from yourselves mates that you may find tranquillity in them; and He placed between you affection and mercy. Indeed in that are signs for a people who give thought.

The following excerpt is taken from “Maariful Quran” vol 6 pg. 732-733:

The object of married life is tranquility for which mutual love
and affection is the key


The present verse has declared that the object of married life of man
and woman is peace of mind. This could be achieved only when there is a
mutual recognition of each other’s rights and a sincere effort to fulfill
them. Otherwise the demand for meeting one’s own rights only will lead
to domestic brawls and shattering of peace. One course for the fulfillment
of these rights could have been to lay stress only on legislation and
imposing laws, as has been done in the case of other rights of the people,
where it is prohibited to usurp the rights of others and after due warnings
the punishments have been prescribed, and it is advised to show
sympathy and sacrifice toward others. However, it is a common
experience that people cannot be corrected only by giving them a set of
laws, unless they are accompanied by nurturing taqwa and Allah’s fear in
the hearts. That is why the Holy Qur’an, whenever it gives any
injunctions regarding the social life of man, comes with the directions of
(Fear Allah) as a complement to those injunctions.

Mutual relations between man and woman are of such a delicate and
sensitive nature that ‘neither a law can ensure the fulfillment of their
respective rights completely, nor can any court do full justice to it. It is for
this reason that the Holy Prophet has selected those verses of the
Qur’an for the khutbah (sermon) of nikah in which stress is laid on piety,

fear of Allah and the Hereafter.

Only these qualities in the spouses could stand as a guarantor for the fulfillment of mutual rights.

In addition to this, Allah Ta’ala has not made the conjugal rights
merely a matter of rules and regulations, but also a natural and
emotional requirement of every man and woman. It is on the same
pattern as the mutual rights of parents and children are safeguarded by
the natural love they have for each other. Allah Ta’ala has filled the
hearts of parents with such a natural love that they are compelled to
protect their children more than their ownselves. Similarly, a degree of
natural love is put in the hearts of children for their parents. The same
thing is done in the case of spouses, for which it is said:

(And He has created love and kindness between you – 30:21), that is, Allah
Ta’ala has not restricted the relationship between spouses to a legal and
religious relationship, but has filled their hearts with love and
compassion. The literal meaning of wudd and mawaddah is ‘liking’,
which results in love and affection.

Here Allah Ta’ala has used two words:

one is mawddah ( love or friendship ) and the other rahmah (kindness).
It is possible that mawaddah ( love ) refers to the young age when
spouses are attracted towards each other with love and affection, while
rahmah refers to the old age when passions subside and compassion for
each other takes over. (Qurtubl)

After that it is said (Surely in this there are
signs for a people who reflect – 30:21). Although this verse has mentioned
only one sign, but at the end of the verse, the word ‘signs’ in plural is
used. The reason for this is that conjugal relationship, which is being
discussed here, has many aspects, religious and mundane benefits. If all
these benefits are taken into consideration, it appears that this
relationship contains a number of signs of the divine omnipotence.

References:

Shafi, Muhammad (2008). Maariful Quran. (Vol .7 pg. 732-733). http://www.islamicweblibrary.com/wp-content/uploads/2020/04/Maarif-volum3-english.pdf