A road to Damascus moment is a change, an important point in someone’s life where a great change, or reversal, of ideas or beliefs occurs.
The term is based on the conversion of Saul in The Acts. As it is written by Luke; God orders Saul to go to Damascus:
And he trembling and astonished said, Lord, what wilt thou have me to do? And the Lord said unto him, Arise, and go into the city, and it shall be told thee what thou must do. – The Acts 9:6
Also, The Conversion on the Way to Damascus is a masterpiece by Caravaggio, painted in 1601 for the Cerasi Chapel of the church of Santa Maria del Popolo, in Rome.
The painting depicts the moment recounted in the ninth chapter of Acts of the Apostles when Saul, soon to be the apostle Paul, fell on the road to Damascus. He heard the Lord say “Saul, Saul, why persecutest thou me? […] I am Jesus whom thou persecutest: it is hard for thee to kick against the pricks […] Arise, and go into the city, and it shall be told thee what thou must do”. And so Saul entered into Damascus and preached in the synagogue that Jesus was the son of God.
This event has been the subject for many a compilation of medieval biblical interpretations, and it has most probably framed the event for Caravaggio.