God Almighty said: "And of His signs is that He created for you from yourselves mates that you may find tranquility in them; and He placed between you affection and mercy. Indeed in that are signs for a people who give thought" [Ar-Rum 21].
Marriage is a sign of the One and Only, following the sign of creation as mentioned in Surah Ar-Rum.
And because life is a mission and a responsibility, God Almighty created for man a mate of his own kind to be a help to him on the path of goodness—a righteous husband and a righteous wife. It is a solid foundation that God has enabled through the affection and mercy He placed between them, to fulfill the purpose of life to which the Creator of all things alluded in His saying: "And it is He who has created from water a human being and made him [related by] lineage and marriage. And ever is your Lord competent [concerning creation]" [Al-Furqan 54]. Thus, He established marriage primarily for the purpose of procreation; it became a sacred, lawful bond that preserves the species which God has honored and maintains the offspring for whose sake the world was created.
God Almighty said, in describing the messengers and praising them: "And We have already sent messengers before you and assigned to them wives and descendants" [Ar-Ra'd 38]. He mentioned this in the context of gratitude and displaying favor.
He also praised His saints for requesting this in their prayers, saying: "And those who say, 'Our Lord, grant us from among our wives and offspring comfort to our eyes'" [Al-Furqan 74].
It is sufficient to consider what was mentioned in the Holy Book about John (Yahya), son of Zechariah, who never committed a sin nor intended one. He was the result of his father Zechariah’s prayer: He said, "My Lord, grant me from Yourself a good offspring. Indeed, You are the Hearer of supplication." While he was standing in prayer in the chamber, the angels called to him, "Indeed, Allah gives you good tidings of John, confirming a word from Allah and [who will be] honorable, abstaining [from women], and a prophet among the righteous."
Imam Ali (peace be upon him) said: "I did not ask my Lord for a child who is fair of face or well-built; rather, I asked Him for a child who is obedient to God and fears Him, so that when I look at him while he is obedient, my eyes may find comfort in him."
The Unitarians (Muwahhidun) say that there are two constraints in Unitarian worship: the constraint of lawfulness and the constraint of moderation. The constraint of lawfulness is refraining from prohibited things, and whoever protects himself from major prohibitions, God forbids the Fire for him. The constraint of moderation is the hallmark of the "middle nation" as God Almighty said: "And thus We have made you a just/middle nation that you will be witnesses over the people" [Al-Baqarah 143].
The moderation of methodology and the temperance of conduct reject the extremism of avoiding what God has made lawful, just as it abhors excess in the practice of the lawful. As some wise men have said: "The greatest disgrace is humiliating the soul to animalistic desire until it becomes a slave to it, and the greatest adornment is training the soul with wisdom and suppressing desire with chastity."
The people of Tawhid (Unitarians) do not uphold the principle of marriage merely to extinguish the fire of desire, even though it provides chastity and protection from the forbidden, and serves as a solution and remedy for many who find no patience in curbing their desires. However, it is not the primary criterion for the matter of marriage, the ultimate goal of which is to seek offspring and uphold the tradition; the pursuit of offspring is intended by nature and wisdom. Thus, desire is of the level of a dependent or an addition, and is not the primary intent, as stated in the interpretation of God's saying: "Your wives are a place of cultivation for you, so come to your place of cultivation however you wish and put forth [righteousness] for yourselves. And fear Allah and know that you will meet Him. And give good tidings to the believers" [Al-Baqarah 223]. What is required from the cultivation is the growth of the crop; likewise, the purpose of coming to women is the pursuit of offspring, not the fulfillment of desire. And although marriage provides chastity, through which one lowers the gaze and guards the private parts from the forbidden, achieving victory in the arena of struggle is done by elevating humanity over instinct. Because releasing the self into the world of desire, even within the lawful, without organization and restriction, is an exhaustion and harm to the body, and a weakening of the soul by clouding the mirror of its insight.
As Galen said: "Excess in intercourse exhausts the body, weakens the eyesight, and corrupts the mind." And it is attributed to Hippocrates the Wise: "Intercourse is like a well; when it is drawn from, it gushes, and when left, it dries up."