Let me first define the term that we are going to discuss. Interracial is defined as, "Relating to, involving, or representing different races" (thefreedictionary.com/interracial). So the interracial marriage would be, a marriage representing different races. One example of this would be (but not limited to) "white" marrying "black." I use this example because when you get down to the meat of the matter, those who oppose interracial marriages only seem to oppose this arrangement.
Before I can answer this question I must answer another important part of the question, where do the "races" come from? You might be thinking, "why is this so important in answering this question?" Let me share with you this, that if you understand where the "races" come from then you will be able to answer this and every other "racial" question that comes our way.
First, nowhere the Bible do we find the term "races," only nationalities, therefore there is only one genetic "race", the human "race." But for the sake of this article I have used the term "race(s)." The Bible is very clear to show us from where we all started. God created one man and one woman. In Genesis 3:20 Moses wrote, "And Adam called his wife's name Eve, because she was the mother of all living." This means that every man and every woman can trace their ancestry back to Adam and Eve. Not just the "white race" or the "black race," but every single person living. Paul wrote, "And He has made from one blood every nation of men to dwell on all the face of the earth" (Acts 17:26). See, "from one blood every nation" and not a bunch of different races or bloods.
I am not a scientist nor do I have a college degree in the scientific field, but I have read at great length what others have researched on this subject. One of the best explanations that I have found was written by the staff at Apologetics Press:
Melanin does far more than simply provide the body with pigmentation. Its most important role is in protecting the body by absorbing ultraviolet (UV) radiation from sunlight that falls on the skin. UV radiation can damage the skin and produce skin cancer if not filtered out by the melanin. People who have large amounts of melanin in their skin are generally very resistant to the effects of UV radiation. People with only small amounts of melanin may suffer badly if exposed to too much UV light. The energy of the UV light penetrates deeper into their skin and can cause damage to the skin tissues.
In humans, production of the skin coloring agent melanin is controlled by two pairs of genes. We can designate them Aa and Bb, the capital letters representing dominant genes and the small letters recessive genes. A and B, being dominant, produce melanin very well; being recessive, a and b produce melanin to a lesser degree.
If Adam and Eve had been “heterozygous” (AaBb; two dominant, two recessive genes), they would have been middle-brown in color. And, from them—in one generation—racial differences could have occurred quite easily.
(apologeticspress.org/apPubPage.aspx?pub=1&issue=422)
I know the previous paragraphs give us a sizable amount of information. The simple explanation is that Adam and Eve were created with all the genes necessary to produce all the different shades that humans beings possess. In other words, we are all of one "race" no matter how much "melanin" we have in our skins. Also, to divide people into "color" categories is disingenuous. Take those that are said to be "white." If I were to line up everyone that claimed to be "white," then I would see all shades. In fact, very few, if any, would actually be "white" as we understand the color.
God designed the "color" through melanin in order to protect us. As we live in areas that have higher concentrations of UV rays, more melanin is needed to protect us. Just the opposite is true for those that live in areas of the world with less UV rays. The closer you live to the equator the more UV rays you receive thus the more melanin you need. The further you live from the equator the less you receive thus the less melanin you need. Can you see God's perfect design?
Finally, God has never classified people into different races. We only read of different nationalities, i.e. where people live. Therefore, since God has not condemned the intermarrying of different nationalities, we are free to marry whom we wish; within the God ordained ordinances of marriage (one man and one woman for life).
Let us look at the people of this world as God does, without partiality. And let us all continue to teach as the Bible teaches, that God does approve of "internationality" marriages because God created us all as one human race. Let this be your ministering message.