Is it possible that a true gospel which is preached must include real repentance in its message?
When the gospel was preached by Peter in the beginning of Acts, repentance was included in the gospel message (Acts 2:38). Repentance means to turn away from something. In this case, a person must turn away from their sin and not repeat it.
A time of confession and repentance must be part of following Christ. Confession comes in two parts. The first is to confess our sin, and the second is to confess (or profess) the Lordship of Christ and him as Savior.
Repentance is part of our confession of sin. As we confess these things we are confessing that we will not do them again. They fall under the blood of Christ in our salvation. Repentance is the call to turn away from these sins so that we can live for Christ. It is part of being dead to send and alive in Christ (Romans 6:1-11: Ephesians 2:1-10).
For this reason, all of these things are part of the confession of faith that leads to following Christ all of the rest of our days. It is a full commitment to live for Christ at all costs. This commitment to Christ means that we must have no other masters of our hearts. Sin can no longer rule over us. This is why repentance is a necessary part of the salvation process.