In Luke 8, a sower threw seeds on four different kinds of ground, and in only one of those types of ground did the seed grow to bear fruit. Since this was a parable, it's applied in the spiritual sense.
You know, I have this bad habit. I sometimes like people, especially if they're, ya know, a pretty, outdoorsy girl or something, and I find myself saying, "Wow, she's got tons of spiritual potential." Now some other girl, maybe a city slicker who hangs out at the bars a lot, well I might find myself saying, "Yeah, no potential there."
What's really going on? Well, my mind is not able to see the spiritual reality of the "soil" of these people, but it's eager to have one be a Christian—for me! "She's make a great Christian...for me." That can be tempting, but remember, we don't know what sort of soil we're seeing, so we need to scatter it evenly, everywhere.
"For the entire Law is fulfilled in in this one word: "You shall love your neighbor as yourself."—Gal 5:14