Marriage holds a significant place among the inevitable events of human life. The fact that those who reject marriage are extremely rare highlights the necessity of married life.
Islam does not accept the view held by some religions that married life is contrary to the spiritual path; on the contrary, it strongly emphasizes marriage.
When Uthman bin Maz'un (RA) sought permission from the Prophet (PBUH) to embrace celibacy (monasticism), the Prophet (PBUH) rejected his request. Sa'd bin Abi Waqqas (RA) stated that had the Prophet (PBUH) granted him permission, they would have resorted to castration.
Sources: Bukhari 5074, Muslim 2488
Some of the Prophet's companions discussed their intentions: one said he would not marry, another said he would pray all night without sleeping, and a third said he would fast continuously without a break. When this news reached the Prophet (PBUH), he asked what the state of those who said such things would be. He then declared, "I fast, and I also break the fast; I pray, and I also sleep; and I marry women. Whoever turns away from my way (Sunnah) is not of me."
Narrator: Anas (RA)
Source: Bukhari – 5063
From the aforementioned Hadith, one can understand how essential marriage is for Muslims.
Islam cites two reasons regarding the necessity of marriage.
"O mankind! Fear your Lord, who created you from a single soul! From it, He created its mate. And from the two of them, He caused numerous men and women to multiply and spread." Fear Allah, in whose name you make requests of one another! And fear Him regarding the ties of kinship; indeed, Allah is ever-Watchful over you. (Al-Quran 4:1)
From this, we learn that procreation is one of the purposes of marriage.
The Prophet (peace be upon him) said: "Whoever among you has the means to bear the expenses of marriage should get married; for marriage restrains the gaze (from looking at other women) and safeguards chastity." Narrated by Ibn Mas'ud (may Allah be pleased with him). Source: Bukhari 1905, 5065, 5066.
This Hadith indicates that protecting oneself from improper conduct is another purpose of marriage.