See Psalm 127:1–2
Saul is a righteous Jew, a Pharisee, instructed in the letter of the law. He has determined that he must destroy the troublesome Christian sect that is causing turmoil in Jerusalem and beyond. He has gained the permission of the high priests to go to Damascus to find and arrest the agitators and bring them back to Jerusalem in chains.
Saul has the authority of the high priests behind him. He has the force of the Hebrew law supporting him, but he is fruitlessly laboring against the will of God. On the way to Damascus, he is stopped by a blinding light and he hears a voice: “Saul, Saul, why do you persecute me?” (Acts 9:4). From that time on, Saul (who would become known as Paul) begins to labor mightily as an apostle of Christ. Until that flash of light near Damascus, Saul was a builder laboring in vain. He was the watchman standing guard over Judaism in vain.
God had a purpose for Paul as He has a purpose for each one of us. But to work within that purpose, we need to stop working against the will of God. Paul was transformed into an apostle by his encounter with Jesus.
What about you? What about me? Are we, like Saul, builders laboring in vain? Or are we fulfilling God’s purpose by working within His will rather than against it?
–Eric Kampmann, Signposts