God created man out of the dust of the earth, and breathed life into him.

Gen 2:7  And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living being.

The life was just physical life, not eternal life, because at death man returns to dust.

Gen 3:19  In the sweat of your face you shall eat bread Till you return to the ground, For out of it you were taken; For dust you are, And to dust you shall return.”

For more information on this see “Do you have an immortal soul?”

Yet, God has created a spirit in man.

Zec 12:1  The burden of the word of the LORD against Israel. Thus says the LORD, who stretches out the heavens, lays the foundation of the earth, and forms the spirit of man within him:

Isa 42:5  Thus says God the LORD, Who created the heavens and stretched them out, Who spread forth the earth and that which comes from it, Who gives breath to the people on it, And spirit to those who walk on it:

At death, the spirit in man returns to God, and the physical body returns to dust.

Ecc 3:20  All go to one place: all are from the dust, and all return to dust.
Ecc 3:21  Who knows the spirit of the sons of men, which goes upward, and the spirit of the animal, which goes down to the earth?

Ecc 12:6  Remember your Creator before the silver cord is loosed, Or the golden bowl is broken, Or the pitcher shattered at the fountain, Or the wheel broken at the well.
Ecc 12:7  Then the dust will return to the earth as it was, And the spirit will return to God who gave it.

What function does the spirit in man serve?  It allows God to search the inner depths of our mind.

Pro 20:27  The spirit of a man is the lamp of the LORD, Searching all the inner depths of his heart.

The spirit in man also imparts intellectual capacity that differentiates man from the animals.

Job 32:8  But there is a spirit in man, And the breath of the Almighty gives him understanding.

The spirit in man allows man to know the things of man.

1 Cor 2:11  For what man knows the things of a man except the spirit of the man which is in him? ….

What does this verse mean?  Let’s consider for a moment, a cow.  Imagine you could talk to this cow.  What could you meaningfully talk about to the cow?  The grass, eating, sleeping, maybe the weather. That’s probably about it.  The cow would not understand the everyday things we do, such as: getting dressed in the morning, going to work or school, having coffee with a friend, listening to music, watching television, going shopping, cooking dinner, planning for a holiday.  These are the things of man, the things which the spirit in man enables us to understand.  A cow does not have the spirit of man and cannot understand these things.  This is what the apostle Paul meant when he wrote: “what man knows the things of a man except the spirit of the man which is in him”.

Some animals have a similar sized brain as man or bigger.  Yet, science cannot explain why man has a far superior intellect than animals.  The spirit in man is the reason for this.

It is worth commenting on the second part of 1 Cor 2:11

1 Cor 2:11  … Even so no one knows the things of God except the Spirit of God.

Just as the spirit in man enables man to understand the things of man, so the Spirit of God enables man to understand the things of God.  In other words, just as a cow does not have a hope of understanding the things of man, so man does not have a hope of understanding the things of God – without the Spirit of God.  Man cannot understand spiritual things through his physical senses alone.  Man needs the Holy Spirit to understand spiritual things.  This is what the apostle Paul meant when he wrote: “no one knows the things of God except the Spirit of God”.

Conclusion

The spirit in man is something that God has created in man, that is not man but rather part of man.  It returns to God at the end of a man’s life.  It allows God to search a man’s heart.  It gives man an intellectual capacity not found in animals.