Immanuel (Immanu-el), read in the European tradition as Emmanuel or Immanuel, is not the personal name of the Son of God, but a symbolic title. It means "God with us". The One whom Scripture calls Immanu-el is the One in whom the presence of God with us, among us, is realized.

The prophet Isaiah, who used this symbolic title, wanted to convey exactly this meaning to us. The personal name of the Savior was hidden from Isaiah, and only to the Immaculate Virgin and Joseph did the Angel give the command to name the Child Jesus. This latter name, like most Jewish names, is also meaningful; it translates as "God saves" or "God the Savior". Such a name was often given to children in Judea (tradition claims that this was the personal name of the robber Barabbas and some others mentioned in the New Testament). In relation to an ordinary child, this name was translated as "God is the Savior of this person".

Given to Jesus, this name acquired its true significance. The Evangelist Matthew, addressing predominantly a Jewish audience, writes that Joseph received the command to name the Child Jesus, and this was in fulfillment (and not in violation) of the prophecy of Isaiah. In the biblical context, this is an almost obvious fact, because the prophecies of the Old Testament are not literal predictions, but a revelation of the meaning of coming events.

In antiquity, the "sons" of something were those who in some way partook of its nature. Thus, people were called "sons of men," the subjects of a kingdom were called "sons of the kingdom," and those who sow ruin were called "sons of wrath"; the "sons of God," therefore, are bodiless spirits who partake of the spiritual nature of God. This designation occurs several more times in the Bible, with the same meaning.

The daughters of men appear in this narrative for the following reason. Marriage in the Bible is one of the most frequent models, an image of the relationship between God and people. Therefore, the "marital relations" of bodiless spirits and the daughters of men are simply paganism: the worship of all sorts of water nymphs and other spirits that are not God. From this, the words of God in  6:3 become understandable and appropriate: "My Spirit shall not strive with man forever".

"Giants," as is clear from the above, are mighty beings whose appearance is associated with the emergence of paganism. We are talking about magicians, priests possessing dark magical secrets, and other sorcerers characteristic of paganism. Such a crowd indeed abounds in practically every pagan religion.

The whole narrative, therefore, speaks of the final falling away of people from God, when humanity begins to worship created beings instead of God, and through magic commits violence against the spiritual and material world. It is quite obvious that such humanity has nothing good to expect, and therefore the flood soon comes.

It is rather curious that you ask this question on a biblical website. But since you have, the answer must be sought not in human experience, but in the Bible.

Let us consider this, then. Certainly, the Bible acknowledges that there is a distinction between man and woman, especially concerning their roles in procreation. Yet at the same time, the Bible never regards a woman as anything less than fully human, and therefore all biblical instructions regarding what a person ought to be apply equally to both man and woman. And these instructions apply primarily not to the physical or psychological qualities of a person, but to the spiritual ones, which are determined by their relationship with God. Therefore, it is written there that it is God who joins people in matrimony (provided, of course, that both place their trust in Him).

The Bible devotes a great deal of attention to this matter. The passages listed below may be considered particularly significant.