In Genesis 6:2 it says,
That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose.
But if angels are spirit than how can they have sex with physical women?
In Genesis 6:2 it says,
That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose.
But if angels are spirit than how can they have sex with physical women?
Short Answer: The available information primarily indicates that they engaged in sexual relations with women. The details regarding the mechanics or "circumstances" of these encounters are not explicitly described. Additionally, it is unclear if further clarification on these matters will be provided from a theological standpoint.
Now, let me give one possible view:
Those who interpret the "sons of God" as non-human spiritual beings or fallen angels often suggest that these beings somehow took on physical form or assumed human-like bodies in order to interact with humans. This interpretation is based on the belief that angels have the ability to manifest in different forms or appearances.
2 Corinthians 11:14-15 NKJV
And no wonder! For Satan himself transforms himself into an angel of light. 15 Therefore it is no great thing if his ministers also transform themselves into ministers of righteousness, whose end will be according to their works.
Further support for this view may be found in:
Hebrews 13:2 NKJV
Do not forget to entertain strangers, for by so doing some have unwittingly entertained angels.
There are also some examples where it seems angels take on the appearance of human men and engage in typical human activities such as eating and conversing.
Conclusion: Some posit that angels have the capability to assume human form. According to this perspective, if angels can manifest physically, it is may be possible for them to impregnate women.
A second possible view:
One interpretation of the term "sons of God" suggests it refers to the descendants of Seth. According to this viewpoint, the lineage of Seth, considered to be faithful followers of God, was drawn to the daughters of Cain's lineage, who were perceived as having strayed from God. This led to intermarriages that resulted in increased wickedness.
Support for this interpretation is primarily derived from Genesis chapters 4 and 5, which document two distinct lines of descent from Adam: one through Cain and the other through Seth. Within the Old Testament, followers of God's covenant are occasionally identified as God's sons
Deuteronomy 14:1 “You are the children of the Lord your God; you shall not cut yourselves nor shave the front of your head for the dead.
Jeremiah 3:19 19 “But I said: ‘How can I put you among the children And give you a pleasant land, A beautiful heritage of the hosts of nations?’ “And I said: ‘You shall call Me, “My Father,” And not turn away from Me.’
The specific term "sons of God" is not directly applied to them. If the interpretation concerning Seth's descendants is accurate, it could provide context for the later prohibitions against Israelites marrying women from Canaan, as seen in Exodus 34:16 and Deuteronomy 7:3.
In terms of biblical hermeneutics, the most direct evidence for angels being able to engage in sexual activities is the episode in Sodom, where the men of the city apparently wanted to rape Lot's guests, who are angels. Lot tried to dissuade the rapists by offering them his virgin daughters. (Gen 19:5-8) Another piece of biblical evidence pointing to sex between angels and humans is found in Jude 1:
6 The angels that did not keep their own position but left their proper dwelling have been kept by him in eternal chains in the nether gloom until the judgment of the great day; 7 just as Sodom and Gomor′rah and the surrounding cities, which likewise acted immorally and indulged in unnatural lust, serve as an example by undergoing a punishment of eternal fire.
The OP wonders how the angels, being spirit, could have sex. For the Bible, this is not a problem. Angels can apparently manifest as bodies that perform physical functions. Angels also ate a meal with Abraham; and an angel wrestled with Jacob, putting his hip out of joint. So the Bible clearly teaches that angels can carry out bodily functions and interact intimately with humans.
How they could successfully reproduce with human women is a more difficult problem. Some commentators admit that angels cannot interbreed with humans because they do not have human DNA. Some affirm instead that demons were involved in the creation of the Nephilim through non-sexual means. Others, with a more scientific bent, think that the episode mentioned in the OP belongs to the realm of mythology rather history. Many simply accept the story of angelic-human reproduction on faith.
Conclusion: The bible teaches that humans can interact intimately with angels. But it does not say how sexual intercourse between humans and angels could result in reproduction. In the end, answer to the OP's question is beyond the scope of biblical hermeneutics, except insofar as the Bible teaches us to believe what it says.
The issue as presented is related to whether or not heaven beings have physicality.
The Bible already makes it clear that heavenly beings can have sexual relations
Genesis 3:15
”I will put enmity between you (the nachash see Rev 20:2) and the woman, and between your offspring and her offspring; he shall bruise your head, and you shall bruise his heel.”“
Thus it is clear that God prophetically anticipates that the heavenly beings though they were not given female counterparts would eventually be tempted and take human women
Genesis 6:2
”the sons of God saw that the daughters of man were attractive. And they took as their wives any they chose.“
With the exception of translations which are interpretations, sons of God only ever refers to heavenly beings in the OT and never to humans.
So then how different are the heavenly beings from humans?
Psalm 8:4-5
”what is man that you are mindful of him, and the son of man that you care for him? Yet you have made him a little lower than the heavenly beings and crowned him with glory and honor.“
Heavenly beings are only a little higher therefore in difference from humans.
1 Corinthians 15:40
”There are heavenly bodies and earthly bodies, but the glory of the heavenly is of one kind, and the glory of the earthly is of another.“
There are only two kinds of bodies, earthly or heavenly. A heavenly being has a heavenly body. It doesn’t need to take on a body as would a bodiless demon spirit (another tangential discussion referring to the Nephilim that had a human and a heavenly parent and who’s name were never written in the book of Life from before the creation).
We know heavenly beings eat food
Psalm 78:25
”Man ate of the bread of the angels; he sent them food in abundance.“
We know that heavenly beings can interact with the natural realm
Acts 12:7
”And behold, an angel of the Lord stood next to him, and a light shone in the cell. He struck Peter on the side and woke him, saying, “Get up quickly.” And the chains fell off his hands.“
To abandon an abode or a dwelling place and to take on an earthly body are two entirely different things and the text does not speak about the heavenly beings in Genesis 6 taking on human bodies. All heavenly beings are referred to in the masculine and all apparitions are of males.
The only other issue you’ll run into is Jesus’ words
Matthew 22:30
”For in the resurrection they neither marry nor are given in marriage, but are like angels in heaven.“
To not be given in marriage does not preclude one from being able to copulate.
And so in summation heavenly beings could interact with the natural realm because they were, in modern language, supernatural. They were not confined to the laws of the natural they are confined to the laws of the supernatural or the spiritual realm. But they can and do interact with the natural. They have bodies, they can eat, they can copyists, they are males, meaning they have male genitalia, they can also walk on water, walk through buildings, do activities that defy the natural laws but they are after all only a little higher than men.
And that’s how it is possible for the heavenly beings to copulate with human women and have halflings, half humans and half heavenly being children that were never written in the book of life from before the creation of the world.
Answer
Angels cannot have sex with human women in any meaningful way for the following reasons:
Explanation
“for you are all sons of God” (Gal 3:26) “There is no male and female” (verse 28).
In the resurrection, there won’t be any gender differences. The tradition is followed from heaven where we don’t see any gender difference among the angels.
“For when they rise again from the dead, they neither marry nor are given in marriage, but are as angels in Heaven” (Mark 12:25).
Question: why did Jesus compare the resurrected saints to angels?
Answer: it is because the angels are asexual. You never see a male angel and a female angel in Scripture.
Some say, Jesus meant the good angels “in heaven” not the fallen angels; the fallen angels can have sex. This is untrue. Sin doesn’t give anyone any extra caliber! Besides, in Scripture we see even the fallen angels in heaven. Satan is standing among the angels of God in heaven (Job 1:6; 2:1). Lying spirit is in heaven (1 King 22:21-22; 2 Chron 18:20-21). By nature, whether fallen or not, angels are asexual.
“Food is for the stomach, and the stomach is for food, but God will make them both unnecessary” (1 Cor 6:13).
This is because in the resurrection there will only be eternal spiritual life not physical life.
If the temporary physical food cycle is destroyed in the resurrection, then definitely the temporary physical sex cycle also will be destroyed.
“Just as sin entered the world through one man” (Rom 5:12).
If angels had sex with human women, then sin would have entered through one man and through several angels! This didn’t happen.
Eve is called “the mother of ALL living” (Gen 3:20). If angels had sex with human women and procreated hybrid offspring, then Eve could not be called the mother of all living.
If the angels had sex with human women, the offspring thus born would be a hybrid species outside the salvation project of God. The Word of God became a full human (Jesus Christ) and atoned for the entire mankind. Jesus didn’t atone for any hybrid species. So they would never be saved.
There is something known as a Species Barrier. If two different species are engaging in sex, there won’t be any fertile offspring. The lineage will not be continued.
Man is created in the image and likeness of God (Gen 1:26); not of angels. So mankind is a different species from angels. They cannot copulate and procreate at all.
Truth of Genesis 6:2
Genesis 6th chapter is a continuation of the 4th chapter. Chapter 5 is just an inset in between. The story continues from chapter 4 straight into chapter 6.
The last verse in chapter 4 says:
“And a son was also born to Seth, and he called his name, Enos. Then it was begun to call on the name of Yahweh.”
There is a marginal reading here that says:
“Then began men to call themselves by the name Yahweh” (various commentaries).
And how did they call themselves?
“Sons of God”.
Why?
“For as many as are led by the Spirit of God, these are sons of God” (Rom 8:14).
This is similar to terms such as “people of God”, “prophets of God”, “saints of God”, “the Church of God” etc.
This was the very first group of people who followed the true God in history under the leadership of Seth. But soon, as usual, they faltered when they married beautiful women from the unbelievers’ camp (Gen 6:2).
It is then God said:
“My Spirit shall not always strive with man” (verse 3).
So Genesis 6:2 is not referring to any angels. The sons of God were a primitive name for the Church of God.
Consider Melchizedek. We know he's not a human because he had no beginning. (Sidenote: some think he was Christ, but scripture says Christ is a priest after the order of Melchizedek... which would be strange if they were the same person. I am taking the assumption that they are different here, but you can research and decide this point on your own).
If the Bible didn't specifically state that Melchizedek was a king and a priest on earth, and someone Abraham was familiar enough with that he gave tithes to him, then who would ever believe that an angel could have been a king on earth?
And who was he a king over? Perhaps men... or perhaps others like himself?
This is why many believe there were angels on earth at that time which had bodies with flesh, and that some of these were the ones spoken of in Genesis and in Jude which engaged in sexual immorality.
This is the view taken in some texts that predate Christ, namely the Book of Jasher and, if I recall correctly, the Book of Adam. I don't mention these books to claim they have any authority, but only to point to the fact that they were written long ago and therefore this view is not a new one as the author(s) must have believed it.