I believe Mises is making a general point about the logic of action.
We are moved to act because we are (relatively) dissatisfied with our present position and believe that by undertaking action A we can reach a more satisfactory position. The nature of the human condition is such that no matter what we have or what we can do, there is always more and better.
So, osgood401, while it’s true that, as you point out, ‘The living are subject to change and therefore [are] not absolute or complete], Mises isn’t only talking about death; what he is also rejecting is the idea that there is any perfect or complete state because in such a state there could, by definition, be nothing more perfect and so no reason to act.
Attempts to consider what life would be like in the presence of God alsmost always comes down to metaphors – the Beatific Vision, etc. Scripture openly admits that what a perfect state would be like is not something that we can currently conceive – ‘Eye has not seen, nor ear heard, nor has it entered into the heart of man what things God has prepared for those who love him.’