What does Genesis 6:3 mean?

This is another fascinating verse which has been interpreted through several different perspectives over the years. It falls in the middle of a paragraph describing how a group known as the "sons of God" took human wives who gave birth to a generation of famous "mighty men."

Taken in direct context, this verse seems to declare that God will not let humans continue to lead such long lives. Perhaps the children of the "sons of God" and human women would otherwise have gone on living an extraordinarily long time. Or perhaps God is merely saying that even the normal lifespan of humans was too long, given the evil that is taking place on the earth. Considering how much evil man is capable of with a lifetime of less than a century, the capacity for evil over many centuries is immense.

In either case, God says that He will not allow His Spirit to remain in man forever. God's Spirit, in this sense, seems to be His "breath of life." Humans cannot live without God's Spirit or life-force; we are dependent on God to continue to exist. Now God declares that He will place a natural limit of 120 years on that mortal existence. Looking at life spans for those born after the flood, this seems to be the case. While not a literal maximum, life spans after the flood rapidly decrease until few live longer than 100 years.

Some have offered an alternate explanation for this verse: that God is declaring His judgment will come on the earth 120 years from the time of this pronouncement. That could be. It is also true, though, that eventually human lifespans decreased to a maximum of approximately 120 years. Joseph, for instance, lives to be 110. Moses lives to be exactly 120 years old, while his brother Aaron lives to be 123.