how does granger explain the difference between a lawn cutter and gardener

From the text:

"The difference between the man who just cuts lawns and a real gardener is in the touching, he said. The lawn-cutter might just as well not have been there at all; the gardener will be there a lifetime."

In this quote we come to understand that the person who cuts the grass, simply cuts the grass. The gardener has a personal relationship with his/her garden. They tend it, watch over it..... and even take care of it when it's not doing well...... there a vested interest, and it's lifelong.