T'shuva's Significant Partners
In chapter 7, Rambam explains why the concept of Free Will is so important in Jewish Life and why the topic is presented specifically in The Laws of Repentance. He says that it is precisely the fact that human beings have Free Will, that there is such a thing as T'shuva. Without real choice on the part of the individual, there would be no meaning to Repentance. If a thief had no choice in his behavior, then he also has no accountability and responsibility for what he does.
But we do have freedom to choose what we do. And therefore, we are accountable for what we do, and there- fore we have the challenge and obligation to change our ways for the better, to do T'shuva.
Rambam then says that not only is T'shuva real because of our Free Will, it is exceedingly important because of how powerful it is. What it is capable of achieving for the individual (the community and the World).
The final three chapters of Rambam's Hilchot T'shuva explore yet another topic - Reward and Punishment, with a specific focus on the World to Come. This too is not a digression from the T'shuva theme of this section of Rambam's Mishne Torah, it is part of the package deal. Free Will with accountability, with reward for mitzvot and punishment for sins, combine to make T'shuva so important.
All three concepts are presented in little 40-pasuk Nitzavim, the sedra that is ALWAYS read on the last Shabbat of the year, the Shabbat before RH.