Adam and Eve were brought together by the Living God, in the Garden of Eden. Let's continue forward in the dialogue regarding the purpose or purposes behind marriage.
As we continue reading in the book of Genesis, God gives His command to Noah and essentially all of humanity. He tells Noah twice to "be fruitful and multiply."
1 So God blessed Noah and his sons, and said to them: "Be fruitful and multiply, and fill the earth. ...
7 And as for you, be fruitful and multiply; Bring forth abundantly in the earth And multiply in it."[Genesis 9:1, 7 NKJV]
Here we see God’s decree for the purpose of humanity, to be fruitful and multiply. To follow this command it requires male and female relationships to pro-create into fruitfulness. We see this example through out the Bible. The function and purpose of marriage, leads to family and the population of humanity to increase. Families are the bedrock of creation and any culture or society. Families hold towns, cities, regions and countries together. As family breaks down, so does all of humanity.
Moreover, I want to point out, God didn't say, "Be fruitful and add." In today's industrialized, post modern society we have this trend and concern regarding over population. All of the non-Biblical arguments as to why people shouldn't have big families, are part of Satan's attack on humanity. Sadly the Church seems to have bought into such propaganda.
China is a perfect example of population control. In fact, their society's motto would accurately be communicated as, "Be fruitful and subtract." With two people having one child this is the reality of what's been taking place for decades. For the people in the United States, it seems a weird reality to have no aunts or uncles, no cousins and no siblings. Yet, even here people are having 1.9 children on average, per household according to Wikipedia. In the 1950's the average woman had four children. What a backwards reality from what God intended for humanity.
Here's one verse that accurately depicts God's perspective regarding children.
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3 Behold, children [are] a heritage from the LORD, The fruit of the womb [is] a reward.
[Psalm 127:3 NKJV]