What does 'Thy people shall be willing in the day of thy power' mean?

This phrase indicates that true willingness to believe and follow God comes not from human effort but through divine intervention. God's power transforms stubborn hearts into willing ones, aligning with His purpose for salvation. John 6:37 reinforces this by stating, 'All that the Father gives me will come to me.' This transformation occurs in the 'day of His power,' showing that God actively works to regenerate the hearts of the elect, drawing them to Himself through His Spirit. Thus, the willingness of His people is a result of God's sovereign grace.