What does it mean to "labor in vain"? God tells us that there is a way to work without striving - there's a way to conduct business without sweating and toiling for outcomes. Outcomes are not based on our performance, they are based on our obedience. His desire is for us to see Him working in our lives. He wants us to avoid looking toward our own performance to receive a desired outcome. Instead, He desires that we be obedient to Him, and He will provide for our needs. This ensures against us thinking that it was by our own hands that we were fruitful.