Writers 
In today's society, marriage and sex are significantly decoupled. These days, it's common for men and women to have children, live together, and even sleep together without ever getting married. Marriage is considered a document that someone signs for governmental benefits, and sex is typically viewed as a pointless physical behavior.
Many Christians have embraced this way of thinking, although it is far from the reality. Unfortunately, the standard advice given by pastors nowadays to unmarried couples who are having sex is to break up (repent), give up sex, and then get married a few months later if both parties are Christians (instead of getting married right away).
God considers sexual union to be a binding covenantal deed and marriage to be a covenant. The marriage agreement is either strengthened, shattered, or refreshed by sex. Most Christians don't think in this way, nor does the secular culture. However, we ought to wish to adhere to God's ways rather than our own. Given the shifts in the culture's sexual and marital norms, it's more crucial than ever to establish a solid theology of sex and marriage.
Initiation of a Covenant as Sex
Sex is a marriage covenant sign, and marriage necessitates the behavior. What is the role of wedding vows, though, is an urgent issue that this brings up? The majority of today's Christians, including most pastors, assert that marital vows in a wedding ceremony are how individuals enter the marriage covenant. However, where does the Bible mention vows at a wedding ceremony? Nowhere is the answer. It is correct that an oath validates a contract, and some people may reply with that statement. But if there is no mention of a verbal oath, then we must presume that the "one flesh" union of a man and woman is an oath-sign, according to Genesis 2:24.
In addition to teaching that sex is the covenant-making sign of marriage, the Bible also teaches that a verbal vow or oath is not required for the marriage covenant. The Bible views sex as a marital and covenantal behavior, in other words. The following are instances in the Scriptures where sexual intimacy is seen as an act that begins a covenant and is the only thing that may make a couple married:
Isaac brought Rebekah into the tent in Genesis 24:67, "and he took Rebekah, and she became his wife." Rebekah became Isaac's wife through their sexual relationship, not through a ceremony.
Jacob planned to wed Rachel, and a celebration was held for them both in Genesis 29:23-25. Laban deceived Jacob that night by giving him Leah, and Jacob "went in to" Leah, which is a euphemism for having sex, making her his wife. Even though he had intended to wed Rachel, Jacob never wavered in his conviction that Leah was now his wife rather than Rachel.
The law in Deuteronomy 21:10-14 states that if a man finds a beautiful woman among the captives and wants to make her his wife, he must let her grieve for one month. He "may then go into her and become her husband, and she shall be [his] wife" (v. 13) after this. The only component of the marriage process mentioned is the man's "going into her."
Deuteronomy 25:5 provides guidelines for a Levirate marriage, in which a brother must wed his deceased brother's childless widow. The brother “shall go in to her and take her as his wife” (Gen 38:8). Once again, becoming married is equivalent to "entering into her."
According to Ezekiel 16:8, God "entered into a covenant" with Israel as a metaphor for a marital "vow" (or "swore an oath"). Although this seems to be a verbal pledge at first, the setting reveals that the pledge is actually the act of sexual union since the woman is "the age for love" and the language employs euphemisms for sex.
It should be obvious from these verses that the Bible considers sex to be covenantal. Sex is a significant act since it is invocational and invokes God as a witness to the agreement between a guy and a woman. The agreement sign does not take place at a marriage ceremony since vows do not establish the covenant. The oath-sign of sexual union establishes the covenant.