The request of the thief on the cross beside Jesus, and Jesus' promise to him, is often used to justify a concept of calling on Jesus for salvation today. However, Jesus' promise to the thief was given under the Law of Moses, before the death, burial, and resurrection that ushered in the law of the spirit of life in Jesus the Christ.
Jesus often forgave sins during His personal ministry, but after His resurrection the gospel was preached on Pentecost by Peter and the other apostles by the power of the Holy Spirit. The gospel message demands faith and repentance, and immersion in water by the authority of Jesus. Public confession of faith that Jesus is the Son of God, the good confession made by Peter, is also part of the response of faith to the gospel message.
Paul makes it clear in Romans 1:16 that the gospel is God's power for salvation, and in 1 Cor 15:1-4, he says that the gospel consists of the death, burial, and resurrection of Jesus. Luke records that repentance and remission of sins would be preached from Jerusalem, and we understand this is a reference to Pentecost and the gospel preached by Peter. Luk 24:45 Then he opened their minds to understand the Scriptures,Luk 24:46 and said to them, "Thus it is written, that the Christ should suffer and on the third day rise from the dead,
Luk 24:47 and that repentance and forgiveness of sins should be proclaimed in his name to all nations, beginning from Jerusalem.
Luk 24:48 You are witnesses of these things.
Luk 24:49 And behold, I am sending the promise of my Father upon you. But stay in the city until you are clothed with power from on high."
The words of Peter on Pentecost seem simple and straight forward: Act 2:32 This Jesus God raised up, and of that we all are witnesses.Act 2:33 Being therefore exalted at the right hand of God, and having received from the Father the promise of the Holy Spirit, he has poured out this that you yourselves are seeing and hearing.
Act 2:34 For David did not ascend into the heavens, but he himself says, "'The Lord said to my Lord, "Sit at my right hand,
Act 2:35 until I make your enemies your footstool."'
Act 2:36 Let all the house of Israel therefore know for certain that God has made him both Lord and Christ, this Jesus whom you crucified."
Act 2:37 Now when they heard this they were cut to the heart, and said to Peter and the rest of the apostles, "Brothers, what shall we do?"
Act 2:38 And Peter said to them, "Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit.
Act 2:39 For the promise is for you and for your children and for all who are far off, everyone whom the Lord our God calls to himself."
Act 2:40 And with many other words he bore witness and continued to exhort them, saying, "Save yourselves from this crooked generation."
Act 2:41 So those who received his word were baptized, and there were added that day about three thousand souls.
The importance of baptism by the authority of Jesus is confirmed by the record of believers at Ephesus who had only received the baptism of John: Act 19:1 And it happened that while Apollos was at Corinth, Paul passed through the inland country and came to Ephesus. There he found some disciples.Act 19:2 And he said to them, "Did you receive the Holy Spirit when you believed?" And they said, "No, we have not even heard that there is a Holy Spirit."
Act 19:3 And he said, "Into what then were you baptized?" They said, "Into John's baptism."
Act 19:4 And Paul said, "John baptized with the baptism of repentance, telling the people to believe in the one who was to come after him, that is, Jesus."
Act 19:5 On hearing this, they were baptized in the name of the Lord Jesus.
Act 19:6 And when Paul had laid his hands on them, the Holy Spirit came on them, and they began speaking in tongues and prophesying.
Obviously, these believers had done what they though was calling upon the Lord for salvation, they had been baptized with the baptism of repentance, having been told to believe in Jesus. However, they had not been taught about the baptism authorized by Jesus, which is a pattern of the death, burial, and resurrection of Jesus.
As we realize that baptism in the name of Jesus involves following the pattern of His death, burial, and resurrection, we can understand that a sinner who has died because of sin is buried with Jesus, cleansed by faith in the power of God, and raised to walk in new life, having received the gift of the Holy Spirit. Teaching that a person is saved before the baptism of faith in Jesus presents a picture of burying someone we are saying is alive. It does not fit the picture: Rom 6:3 Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death?
Rom 6:4 We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life.
Rom 6:5 For if we have been united with him in a death like his, we shall certainly be united with him in a resurrection like his.
Rom 6:6 We know that our old self was crucified with him in order that the body of sin might be brought to nothing, so that we would no longer be enslaved to sin.
Rom 6:7 For one who has died has been set free from sin.
Rom 6:8 Now if we have died with Christ, we believe that we will also live with him.
When Paul writes that those who call upon the Lord will be saved, Romans 10:13, he fully realizes that he has already taught how one calls upon the Lord by obeying the gospel commands of repentance, confession, and immersion. Obviously, we call upon the Lord for salvation by doing the simple and necessary things He commands. It is not doing the things that saves us, but God has always counted obedience as faith. When we obey a simple command like confession that Jesus is the Son of God, and are immersed in water as commanded, we show our faith, and call upon the Lord for salvation.
We are saved by grace through faith, cleansed by the blood of Jesus shed on the cross for our sins. However, faith includes simple obedience, just as was required of Israel when they marched around Jericho 13 times, Naaman dipped in the Jordan river 7 times, and Israelites bitten by the firey serpents had to look at the brass snake in order to be healed.
Telling people that they are saved by praying a prayer of repentance, and putting off baptism until it is convenient, does not follow the story of the gospel. Surely it is time for believers to return to the story of the gospel, 1Co 15:1 Now I would remind you, brothers, of the gospel I preached to you, which you received, in which you stand,
1Co 15:2 and by which you are being saved, if you hold fast to the word I preached to you—unless you believed in vain.
1Co 15:3 For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures,
1Co 15:4 that he was buried, that he was raised on the third day in accordance with the Scriptures,
The idea that we are saved by faith only should be defined. We are saved by submitting our will to God, in faith. Without submission, there is no saving faith. Without repentance, confession, and immersion, there is no saving faith.