Soter is the Greek word for saviour — a rescuer, a deliverer, one who brings people to safety. It was a lofty title in the ancient world, claimed by kings and emperors. The New Testament gives it to Jesus, whose very name (Yeshua) means the LORD saves. The angel announced at his birth, unto you is born this day... a Saviour, which is Christ the Lord.
The related word soteria means salvation, and the study of it is called soteriology. Jesus is Saviour because he saves his people from their sins — not merely from circumstances or enemies, but from the deepest peril of all. There is, Peter declares, none other name under heaven given among men, whereby we must be saved. To call Jesus soter is to confess that rescue comes from him alone.
Soter in Scripture
For unto you is born this day in the city of David a Saviour, which is Christ the Lord.