I'll first explain some ideas behind the Jewish notion of marriage and why it's essential, and then refute some common arguments against getting married.
One of the main reasons for getting married is to help each other grow through a life-long process of emotional, intellectual and spiritual sharing and challenge. This is the meaning of the verse, "It is not good, this state of man's being alone; I will make a helpmate opposite to him" (Gen. 2:18). As long as a person is single, it is not good — meaning not only is the person incomplete, but the entire Creation is also lacking perfection (Rabbi S. R. Hirsch). The purpose of this union is that each should help the other reach perfection. Sometimes this is achieved by sharing; sometimes by opposing, questioning and challenging. This ideal dynamic of "opposing-helpmate" is best achieved between a man and woman committed to a love for growth together for life.
Marriage as context for growth is also intimated by the verse, "Therefore a man shall leave his father and mother and cleave to his wife and they shall become one flesh" (Gen. 2:24). As father or mother, a person's main responsibility is to ensure that the child grow to be the best person possible. Marriage, then, takes a person to the next, natural and higher plane of potential perfection. Becoming 'one flesh' is an allusion to this fusion of two perfect halves into a unified whole. In fact, the Zohar (Lech Lecha 91b) teaches that every soul is divided into male and female components before being sent into the world. Ideally, every match is the 're-fusion' of the halves into one.
But this becoming 'one flesh' is not only figurative. Contrary to popular misconception, Eve was not necessarily created from Adam's rib. According to a statement of our Sages Adam was split in two. The Talmud (Eruvin 11) explains the verse, “And G-d took one of his sides”, to mean that Adam was originally a composite of both male and female aspects side by side. G-d separated them in order to create the longing for, and fulfillment in, the male/female union. Therefore, marriage is the venue through which one attains spiritual, emotional and physical unity and perfection.
Of course, the true pinnacle of male/female physical unity comes to fruition in the birth of their children — another reason to marry. Thus, G-d simultaneously commands and confers blessing upon the union of man and woman, "Be fruitful and multiply" (Gen. 1:28). However, the point is not just to have children. Being 'fruitful' means realizing one's potential through sharing and challenge in marriage, in order that one's productive traits and talents ripen, and his branches become laden with sweet and pleasant fruits. Only then can one truly 'multiply', as his perfection through marriage is conferred to and perpetuated by their children, the fruits of their labor. In this way, a married couple's figurative unity as 'one flesh' becomes manifested literally in one flesh, many times over.
Some people object to getting married because, they argue, as the divorce rate gets higher and higher, why marry to get divorced? In truth, if people really knew themselves and truly understood the purpose of marriage — in short, if each person strove to become as perfect a half as possible — before 'tying the knot', marriage would strengthen the knot, not undo it. Some consider marriage restrictive. Is permissive truly desirable? In any case, one who desires only to receive might find marriage restrictive; one who desires to give will find marriage limitless. Others claim marriage limits one's horizons experientially, career-wise, etc. However, the commitment and obligation to spouse and children provide an opportunity to attain true greatness precisely because of the need to succeed as both a person and professional.
Finally, some resist marriage for global considerations — to alleviate mother earth's over-burdened
