Cast behind a dark life?

Hello,

I'm translating a topic about the knight templar, and here comes the problem as I'm not quite sure about the message;

It says 'To all the profressed knights, both in winter and in summer, we give, if they can be procured, white garments, that those who have cast behind them a dark life may know that they are to commend themselves to their creatorby a pure and white life'

Does the bold sentence mean if the knight were killed or dead, they would be sent to God with pure life ?

Thanks a lot for any help