In the immediate context (based on verse 8), reaping in Galatians 6:9 appears to refer to salvation.
Galatians 6:8-9 (NASB)
8 For the one who sows to his own flesh will from the flesh reap corruption, but the one who sows to the Spirit will from the Spirit reap eternal life. 9 Let us not lose heart in doing good, for in due time we will reap if we do not grow weary.
In a commentary that I read by John Macarthur, however, he stated that "eternal life" in verse 8 is referring to the quality of eternal life (i.e., rewards in heaven), but he didn't make a supporting argument. Is there any support for this argument, or does the reaping in verse 9 refer to salvation?