Charles Spurgeon once said that if you want to set a house on fire you should start the fire in the basement ... because fire burns upward. He was referring to the strategic nature of reaching the poor and broken of a city with the Good News of the Gospel. Spurgeon contended that as the poor of a city were reached that the fire of the Gospel would burn "upward" to the rest of the city.
This is one of the reasons why Spurgeon, while still in his early twenties, was pastoring the largest church in England in one of the worst parts of London. He reached the poor people of South London and the fire burned upward to the rest of the city.