Why has God given believers the Holy Spirit?
God has given believers the Holy Spirit so that they might know the things that are freely given to us by God. The Spirit reveals the things of God, which the unsaved cannot comprehend, and opens the book to those born again, making these truths understandable.
Les explains from verse 12 that believers have received, not the spirit of the world, but the Spirit which is of God, so that they might know the things freely given to us by God. He points out that no one, not even the most intellectual, brilliant, or highly educated, can really know the things of God unless the Spirit reveals them. The unsaved person cannot comprehend these things; they are a closed book. But once a person enters into salvation and is born again by the Spirit of God, the book opens up. Les describes how people say it is like a huge light bulb turned on, and he says the Spirit did it, making these things understandable. Paul did not put them through grade school, high school, and college; he preached Christ crucified and risen from the dead, and the Spirit enables them to know what is freely given by God.
Now we have received, not the spirit of the world, but the spirit which is of God; that we might know the things that are freely given to us of God.