Answer:
The scripture in question is at:Galatians 6:7+8
"Do not be deceived: God cannot be mocked. A man reaps what he sows. The one who sows to please his sinful nature, from that nature will reap destruction; the one who sows to please the Spirit, from the Spirit will reap eternal life." (NIV)
It's meaning is this:
When we plant a garden, we sow(plant) certain seeds in the ground.
When we 'sow' yellow beans, for instance, we expect to REAP(harvest) yellow beans a few weeks later. We would NOT expect to sow yellow bean seeds, and reap cucumbers.
We REAP what we SOW.
The same is true spiritually.
If, in our lives, we 'grow' things that are displeasing to God, if we center our interests on selfish worldly pursuits and ignore spiritual things, we will reap the emptiness that often comes from this lifestyle, along with God's disapproval, and ultimately death.
Whereas, if we 'sow' our lives by seeking out what God wants (Matt 6:33), we will reap a clean conscience, a relatively balanced life, and the reward of everlasting life from our God.(John 17:3)
Jesus used an illustration that applies to this question at Matt 7:16 when talking about the false religious leaders of his day, saying that we would be able to recognize what they've been sowing spiritually, by the 'fruit' they bore...namely unrighteousness.
Again we're given a good example of this at (1 Corinthians 6:9, 10) showing that sowing with a view 'to the flesh' (or spending our time growing unhealthy habits) would provide the harvest of God's disapproval, along with all manor of heartaches which accompany these lifestyles.