If God told you that you could guarantee your brother/father/sister/mother's salvation by running 10 miles per day, every day, for the rest of your life, would you do it? Would you even have to think twice? "Where do I sign?" is the first thought that comes to mind. Daily physical exhaustion to guarantee eternity in Heaven for someone you love? The two can hardly be compared. There's just about nothing we wouldn't do if it came with a guarantee for someone else's salvation.
This is a comforting thought as we live the struggle that is being Christ's chosen in this crazy world. While it's not meant to be taken literally -- of course no work like running (or any other human work, for that matter) can save anybody, let alone one of their family members -- it's a thought to keep tucked away in your memory banks, to pull out and think about when things get tough.
We would gladly do any number of things to guarantee anyone's salvation. Salvation is not up to us, though. It's God's. Alone. He is the Author of salvation. But your efforts come with a guarantee -- His Word will not come back to Him without bearing fruit. So give out the Word and keep running the race. You don't know what your race path will look like once we're in the Lord's presence, looking back on our lives. You don't know who is reading your tracts, reading your blog, watching how you live, or listening to your sermons. Keep on running the race.