Acts 2:21 says, "And it shall be whoever shall call upon the name of the Lord shall be saved."  How does one call upon the name of the Lord?  To call upon the name of the Lord is to call upon His authority.  Let me give you an example.  Suppose a bank robber has just robbed a bank and is running out of the bank with the money.  A policeman sees him and shouts to him, "Stop in the name of the law".  The policeman is basically saying to stop by the authority of the law.  To stop in the name of the law is to stop by the authority of the law.

     What did Peter and rest of the apostles tell them they must do in order to call on the name of the Lord?  Acts 2:37-41 says, "Now when they heard this, they were cut to the heart, and said to Peter and the rest of the apostles, Men and brethren, what shall we do?  38 Then Peter said to them, Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit.  39 For the promise is to you and to your children, and to all who are afar off, as many as the Lord our God will call.  40 And with many other words he testified and exhorted them, saying, Be saved from this perverse generation.  41 Then those who gladly received his word were baptized; and that day about three thousand souls were added to them."

     The question was asked, what shall we do?  They were told to repent and be baptized for the remission (forgiveness) of their sins.  Could their sins be forgiven if they refused to repent and be baptized?  No.  Did they gladly do what they were instructed to do?  Yes, "they that gladly received his word were baptized".  In fact on that one day 3000 people repented and were baptized for the forgiveness of their sins.

     Let's look at another scripture which will help us see what it means to call on the name of the Lord.  In Acts 22:16 Saul of Tarsus (who later became the apostle Paul) was told, "And now why are you waiting?  Arise and be baptized, and wash away your sins, calling on the name of the Lord."  Here Saul of Tarsus was told that if he would "Arise and be baptized, and wash away your sins" that he would be "calling on the name of the Lord".  By being baptized one is calling on the name or authority of the Lord to forgive him of all his sins and to save him.