What the Bible says about Receiving Spirit in Man
(From Forerunner Commentary)
It is likely that "wind" is not properly translated. It should be rendered "spirit," which fits better with the context of verse 5.
"How the bones grow in the womb" is an illustration of how ignorant mankind is regarding even something so close as a child in the womb. Which of us knows when God gives a human being the spirit in man? Is it at conception or when the child takes its first breath? As far as we know, God has not revealed it in His Word. This is similar to Solomon's argument here. He did not know either.
There is much in life that we do not know. There are parts of life in which we must wholly trust God's manifold wisdom and care of each of His creatures because we do not know what He has in mind within His purpose. And His purpose is the key.
John W. Ritenbaugh
Ecclesiastes and the Feast of Tabernacles (Part 2)