“Which name of the Lord do we have to call on to be saved?”
“For whosoever shall call upon the name of the Lord shall be saved” (Rom. 10:13).
The Lord had many names, but Paul is quoting Joel 2:32 here, where the name “Lord” means Jehovah. In Romans 10:13, the name we “call” on today (1 Cor. 1:2) is “Jesus Christ our Lord.”
Calling on the Lord’s name means different things in Scripture. After God stopped speaking to men directly, as He did with Adam and Cain, “then began men to call upon the name of the Lord” (Gen. 4:26). That means calling on His name can mean to pray (Zech. 13:9) and ask God for things (1 Kings 18:24,36,37; Psa. 116:4). Or it can just mean to know Him (Psa. 79:6; Jer. 10:25).
But in Joel 2:32, we know that it means to believe the gospel, for Joel predicted that whoever called on the LORD would be saved. But when Peter quoted Joel (Acts 2:21), he went on to say that whoever would repent and be baptized would be saved (Acts 2:38). Paul likewise makes clear that calling on the Lord’s name (Rom. 10:13) means to believe the gospel (Rom. 10:11), only today the gospel is “the word of faith” that Paul preached (10:8):
“That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised Him from the dead, thou shalt be saved” (Rom. 10:9). source