Poenitentiam agite is in the first of Martin Luther’s 95 Theses. I am not a Latin scholar but it has to do with the idea of repentance and how Christians ought to live a life of repentance. I can appreciate the idea but in our study of Mark the real deal seems to be repent and believe. I think Christians can get twisted around on this by thinking that one must repent (turn his life around) and believe and the repentance thing is somehow a separate act from believing. I think repent and believe are bound together and cannot be separated on a time line.
Belief that saves means that a person understands that they are bad off because of sin and that they are destined for severe punishment as a consequence and, that Jesus has already suffered and died in our place for his wayward life. Belief that saves means that the person is all in on trusting that Jesus took his punishment and that he wants forgiveness for the past and the eternal abundant life that Jesus offers. It is true a person may still have to deal with personal failure and some sins seem to cling to a person but this kind of belief sets a person on new path of life—abundant life.