"Jesus is Lord" is probably the earliest Christian confession. Paul, writing to the Romans, refers to it as a key indicator of salvation:

"if you confess with your mouth, 'Jesus is Lord,' and believe in your heart that God raised him from the dead, you will be saved. For it is with your heart that you believe and are justified, and it is with your mouth that you confess and are saved." (Romans 10:9-10 NIV)