If you are saved from your sin it is because you heard the gospel Paul teaches in 1 Corinthians 15:1-4 that Jesus died for your sins and resurrected according to the scriptures.
There is no other way to be saved today except through the shed blood of Christ as payment for your sins.
However, this was not the gospel taught by the twelve during Jesus’ earthly ministry.
Notice in Matthew 10:5-6 that Jesus sends out his disciples to avoid the Gentiles and preach to Israel only. In verse seven this is the message they were preaching to Israel only:
“And as ye go, preach, saying, The kingdom of heaven is at hand.” – Matthew 10:7
This was known as the gospel of the kingdom (Mark 1:14-15). It wasn’t until later that Jesus first mentioned his death.
“From that time forth began Jesus to shew unto his disciples, how that he must go unto Jerusalem, and suffer many things of the elders and chief priests and scribes, and be killed, and be raised again the third day. “ (Mat 16:21)
To this Peter responded negatively rebuking the one he just identified as the Son of God (Mat 16:22).
It was obvious that Peter did not want Christ to die and was ignorant of its meaning (Luke 18:34).
Peter was among the close circle of disciples selected by Jesus and is no doubt a member of the faithful remnant of Israel. Yet we can learn from these verses that his faith was neither in Jesus’ death for his sins nor in his resurrection for justification.
To put it plainly the gospel that Peter believed unto salvation was not the gospel that Paul presents later to us for salvation.
We must also understand that though we understand now the glory that is found in the preaching of the cross, this was not the glory that was preached by the twelve during the earthly ministry of Jesus.
Instead they preached the glory of the coming kingdom and its king Jesus. Nowhere in this good news of the kingdom is the preaching of the cross.
The secret of the cross was kept secret since the foundation of the world. This mystery was first revealed to Paul in what he calls the revelation of the mystery (Col 1:25-26).