"Through" or "for"?

39 And all these, having gained approval through their faith, did not receive what was promised, Hebrews 11:39 NASB

39 These were all commended for their faith, yet none of them received what had been promised, Hebrews 11:39 NIV

In the first translation mentioned above, the heroes listed in Hebrews 11 gained approval (were commended) through their faith.  In the second translation, they were commended for their faith.

The Greek word translated as "for" and "through" is διά (pronounced dia).  It actually forms the root of the English word "diameter", which is the line that stretches from one side of a circle through to the opposite side, hence why it's translated as "through" in the NASB.  Its meaning is "A primary preposition denoting the channel of an act" (for more information, go here).  So you could say the word "dia" specifies the means by which something is accomplished.

The wording is important because using the word "for" gives the impression that faith is something we do that deserves merit.  But our faith does not deserve merit because whatever faith we exercise is given by God.  That is why the disciples pleaded with Jesus, saying "Increase our faith!" (Luke 17:5) and Paul wrote to fellow Christians,

29 For to you it has been granted for Christ’s sake, not only to believe in Him, but also to suffer for His sake,  Philippians 1:29 (emphasis mine)

And again he wrote in Romans,

3 For through the grace given to me I say to everyone among you not to think more highly of himself than he ought to think; but to think so as to have sound judgment, as God has allotted to each a measure of faith.  Romans 12:3 (emphasis mine)

Faith is like a muscle.  I can go to the gym to workout and gradually my muscles will increase in strength.  But I had to be given some amount of muscle to start!  Thank God for the faith that you have and if you find yourself in a time of little faith, ask God to increase it.