If I commit a mortal sin, I lose sanctifying, or habitual, grace, not all grace, whereas prayer, repentence and other good deeds are done with the help of actual grace.
It is not necessary to be in a state of sanctifying grace to do an action with actual grace.
I hope this was helpful, Benedicat Deus,
Latinitas
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.