On the day of the Lord—the day when God intervenes in history—there will be salvation for those who call on his name and judgment for those who do not. In citing this prophecy, Peter is drawing a connection between the Lord and Jesus Christ (see Acts 2:38). To call on the name of the Lord is thus to invoke the name of Jesus in faith, to trust that he is the Christ who came to deliver God’s people from their sin.
21 And it shall come to pass that everyone who calls upon the name of the Lord shall be saved.’