"Flipping houses"? It's the practice of buying up dilapidated real estate, fixing it up and then renting or selling it for a profit.
Once (long ago) when I started a business I had no start-up capital so I made one product, sold it and bought materials to make two more, etc. until I had a warehouse full of product to ship to fill customer orders. People who "flip houses" can start with one house and plow the profits back until they have a profitable enterprise going.
I was thinking about this principle recently when I realized that "flipping hearts" for the Kingdom is much the same. One at a time "flipping hearts" requires the investment of time and love for Jesus' sake. One at a time God changes hearts and multiplies our efforts and His life-change to build His Kingdom one heart at a time.
"Flipping houses" takes stuff like bricks and morter, paint and wood and lots and lots of hard work. "Flipping hearts" is much the same! It takes a willingness to boldly love other people for Jesus just like He did when He walked this earth wearing our skin and living in our neighborhood. (John 1:14, The Message) He touched blind eyes and ears. He healed lepers. He spoke or reached out a hand to the dead. He commanded evil spirits to go away and much more.
Jesus got involved in intensely personal ways in people's lives appropriate to their need. In doing so, Jesus modeled His plan for building His Kingdom on earth. It is one heart at a time just loving people at their point of need, and He does the rest! That's God's plan for restoring hearts and lives as He builds His Kingdom one heart at a time!