What does “spirit" mean?
In Genesis 6:3, the Hebrew word used for "spirit" is רוּחִ֤י (ruhi). This same word also appears in Job 9:18 and in this passage should unquestionably be translated as "breath." In this passage, Job uses this word to refer to his own breath.
"Indeed, I know that this is true. But how can mere mortals prove their innocence before God?" ... He would not let me catch my breath but would overwhelm me with misery."
In fact, רוּחִ֤י (ruhi) is frequently translated as breath and it can be translated as spirit, wind or breath. When used in connection with God, the אֱלֹהִ֑י ר֣וּחַ (Ruach Elohim) or Holy Spirit can be thought of in any or all contexts. The Holy Spirit (aside from being a spirit) often brings a message from the Lord - she acts as the Lord's "breath" or speech. Likewise she also acts as God's force, power or strength to act upon the world - The wind (power) of the Lord.
Is it the Holy Spirit or is it "the breath of life” that is referred to in Genesis 2:7
In Genesis 2:7, scripture states that Man was brought to life by "breathing" it into man. While this is not the same word used for breath in Job 9:18 or a conjugation and shares no root with רוּחִ֤י (ruhi), it is doubtful that the fact that both words share a meaning is merely coincidental. Just as God gives us life, by breathing into mankind, so he shortens mankinds life by removing his breath (spirit) from mankind.
What was the reason(s) for "the spirit” not remaining in humans?
This question is much more difficult to answer. My opinion is that the reason for this lifespan shortening is for the same reason that God sent the flood. It is my belief that in order to understand the reason for the shortened lifespans, you must first understand who the נָפִיל (Nephilim) and האלהים בני (bene ha'elohim) were. The translations of these words are tenuous based on archaic words that translators and lexographers really aren't sure how to translate, but if my theory on this is correct, the reason had to do with idolatry which came about through the intermarriage of Hebrew and surrounding peoples. This then is the ultimate basis for the shortened lifespan and ultimately the flood.
