Can anybody explain according to the scripture with out any own explanation
1. The first thing to note is that the book of Genesis (which is in the Torah) is
divine revelation. God gave those words to Moses, and he recorded them exactly as given.
And God provided us with the barest of details in this context.
2.
The next thing to note is that only angels are called "sons of God" in the Old Testament (Genesis and Job). That is because they are direct creations of God (no mothers involved). The Old Testament saints are never called "sons of God" but simply "righteous". Job is a good example in that he could have been called a son of God (along with Noah and Daniel) but they are simply designated as "righteous". It is only in the New Testament that human beings are called sons of God after the New Birth (John 1:12,13 and other passages).
3. The third thing to note is that throughout Scripture angels are presented as
masculine spirit beings who appear to human beings as ordinary men.
4. The fourth thing to note is that in Genesis 6, "sons of God" are CONTRASTED with "daughters of men"
because they are essentially different.
5. The fifth thing to note is that because of the sexual union of these angels with human women,
the offspring were unusual -- giants or Nephilim: There were giants [Nephilim] in the earth in those days; and also after that, when the sons of God came in unto [cohabited with] the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown. (Gen 6:4)
What is this verse teaching? 1. Before the Flood there were giants on the earth. 2. When the evil angels had sexual relations with human women, their children were (a) giants, (b) mighty men, and (c) men of renown.
How do we know that these "sons of God" were evil angels? We are told that in the New Testament.
And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day. Even as Sodom and Gomorrha, and the cities about them in like manner, giving themselves over to fornication, and going after strange flesh, are set forth for an example, suffering the vengeance of eternal fire. Likewise also these filthy dreamers defile the flesh, despise dominion, and speak evil of dignities. (Jude 1:6-8)
[NOTE: Jude connects the evil angels with Sodom and Gomorrah and their sexual sins (fornication, going after strange flesh) by using the terms "even as" and "in like manner". Then he connects that with the false prophets who defile the flesh with "likewise"].
For if God spared not the angels that sinned, but cast them down to hell, and delivered them into chains of darkness, to be reserved unto judgment; And spared not the old world, but saved Noah the eighth person, a preacher of righteousness, bringing in the flood upon the world of the ungodly; And turning the cities of Sodom and Gomorrha into ashes condemned them with an overthrow, making them an ensample unto those that after should live ungodly... (2 Peter 2:4-6)