Did Aquinas Believe in the Finish Work of Christ?

The following is from The Warrior Christ: A Theology of the Work of Christ by Owen Strachan:

(Thomas Aquinas) argued for a medicinal atonement approach to divine punishment for sin. Christ did not die for sinners in legal sense, but rather to pay a debt to God and to instigate a “remedy for the avoidance of sin.” This entails that a Christ’s death pays the penalty of our original sin in Adam, but it does not result in a legal righteousness that is imputed to us through saving faith. 

The atonement deals with our Adamic problem, but to overcome our own sins, we must perform acts of penance that — effectively— remedy our personal sin. In the simplest terms, Christ deals with the problem of our sinful nature, but we must deal with the problem of our ongoing sins. In this formulation, the cross does much of the work needed to atone for sins, but not all. The finished work of Christ is not finished.