Galatians 6:7-9 (NKJV)
Do not be deceived, God is not mocked; for whatever a man sows, that he will also reap. For he who sows to his flesh will of the flesh reap corruption, but he who sows to the Spirit will of the Spirit reap everlasting life. And let us not grow weary while doing good, for in due season we shall reap if we do not lose heart.
My pastor gave a four point sermon one time called the Law of the Harvest. The first point is that you reap when you sow. In other words, if you don't sow, you won't reap. The second point is that you reap what you sow. You are not going to get corn if you plant beans. The third point is that you reap more that you sow. Consider the difference in mass between the handful of seed that were planted and the many basketsful of produce that results. This, to me, is truly a miracle. How does that little seed know how to take dirt and air and water and make a cucumber? The last principle is that you reap later than you sow. Little children have a difficult time with this one. You go to all the effort to till and plant a garden but you can't get up the next morning and find a plant growing. It takes an entire season to produce the crop.
Certainly, the implications of this verse swing both ways. J. Vernon McGee relates this story:
One day a visitor in a penitentiary passed by a cell where a man was patching his prison garb with needle and thread. The visitor, wanting to begin a conversation with the prisoner, said, "What are you doing? Sewing?" The prisoner looked up and replied, "No, reaping!"
This Law of the Harvest and this verse have obvious implications in our lives. Many have related this to giving. Indeed, Paul had this very thing in mind since the context of this verse is in sharing one another's burdens. Jesus confirms the principle in the following verse.
Luke 6:38 (NKJV)
Give, and it will be given to you: good measure, pressed down, shaken together, and running over will be put into your bosom. For with the same measure that you use, it will be measured back to you.