‘And they lifted up their voices, saying, “Jesus, Master, have mercy on us.” '
These men pleaded in loud voices for Jesus to show His compassion to them, acknowledging Him as ‘Master' (Epistata - the One who stands over). This title is usually only used by Luke as spoken by disciples of Jesus, and the idea may be in order to demonstrate their interest in His message. It is one of the words Luke uses instead of Rabbi because of his Gentile readers.
Men crying to Jesus for mercy is a theme of the Gospels, for He is the compassionate and the merciful. Compare Luke 16:24; Luke 18:38-39; Matthew 9:27; Matthew 15:22; Mark 10:47-48.