The Greek word for bad literally means evil. It is clear that Jesus was not speaking simply of the physical eye. His concern was for the spiritual health of the disciples. The evil eye has to do with envy over money matters. When money becomes a priority in a disciple's life, it snuffs out the lamp of the gospel and turns it into utter darkness.
Prosperity aborts Christian discipleship.
No one can serve two masters. Either he will hate the one and love the other, or he will be devoted to the one and despise the other. You cannot serve both God and Money. The two words serve and masters refer to a slave's relationship to a slave-owner. Jesus means that one cannot serve two masters equally well or at the same time.