3 ¶ And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.
God declares His intentions to limit the lifespan of man from hundreds of years to a hundred and twenty. This does not mean that every man will live that long but merely gives a general and average upper range nor does it mean that this is immediate but we see it happening after the Flood. Men still live a long time after the Flood but the lifespan continues to decline. There are noteworthy examples of men living longer than that.
The Holy Spirit, when referring to God, uses the word spirit, lowercase s, for intentions and attributes that do not signify the person of God.
For instance, Isaiah 11:2 And the spirit of the LORD shall rest upon him, the spirit of wisdom and understanding, the spirit of counsel and might, the spirit of knowledge and of the fear of the LORD;
Contrast that to God’s Spirit, which is His presence, as all three parts of God can be represented by that Spirit.
Genesis 1:2 And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.
Romans 8:9 But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his.
Luke 4:1 And Jesus being full of the Holy Ghost returned from Jordan, and was led by the Spirit into the wilderness,
It is interesting to note that while God the Father, Christ, and the Holy Ghost are all referred to by the pronoun “he” that the Spirit, the vehicle by which God operates in the world and in the believer, can be called “it.”
Romans 8:16 The Spirit itself beareth witness with our spirit, that we are the children of God:…26 Likewise the Spirit also helpeth our infirmities: for we know not what we should pray for as we ought: but the Spirit itself maketh intercession for us with groanings which cannot be uttered.
Anyway, this spirit, spoken of as not always being in contention against man, who lives a long time and whose bloodline is polluted by the fallen sons of God and the rebellious attitude of Cain, will reduce the average upper range of man’s lifespan. This is something that is ongoing. Today we typically regard average lifespan as including infant mortality, which can lower it significantly, but it is important to consider that, in spite of all of our modern medical advancements, as biologist R.C. Lewontin explained, “In the last 50 years, only about four months have been added to the expected lifespan of a person who is already 60 years old,” if you take out infants who die under one year. (24)
(24) R.C. Lewontin, Biology as Ideology: The Doctrine of DNA (New York: Harper Collins, 1991), 42.