This is the preacher speaking to the congregation and belong to the poetic books. The book of Ecclesiastes has as its central theme that life is vanity of vanities with a calling that is simply to glorify God as God leads them to glory with His Word that is a goad and like a nail that fastens!
The preacher speaks to the congregation (which is given from one Shepherd) It unmistakably speaks to the Shepherd's people. The Lamb of God who lays His life down for them, their entrance and door. It is always the Word of God revealed to us always in Christ! God, who through Christ by His Word and His Spirit guides His people and this Word comes to His church in the darkness of this world that is vanity (the measurement of man's life.) Amid that vanity, the Lord speaks to His people WISDOM!
God through Christ comes with His Word and gives content, or meaning, and purpose to our life! He arms His church with the words of the wise even though the world and the darkness cannot comprehend it. He takes away the emptiness and gives purpose. What is there apart from God and the Kingdom?! God speaks His Word and they are as goads and nails that fasten. A goad is a prod that a farmer uses to "encourage" his animals. Nails have not changed in their history. A carpenter uses a nail to fasten so that it does not come apart. And the Words of wisdom is a goat and nail to us in our life! The Word of God is designed to be a goad and to lead us and prod us to a sanctified life and to sanctified living! Like the animals, we too don't take to kindly to it also, but it spurns us on to Godly living! It helps us NAIL things down in life and we can "hang our life on it!" It leads us, defends us, spurs us on that we have purpose and can live by it! There are some shepherds that take this away and scatter the sheep, but we have "THE SHEPHERD'S Words in the Bible!
It is the ONLY think of value in this realm of vanity. What can you give to your children that has any value? That has any LASTING value? It leads us, it guides us, and spurs us on to a sanctified life and living that will lead on to lasting glory. It prods us, and nails us....so that we can hang our very life on it!