When John Wesley was eighty-seven years old (in 1791) he wrote to Wilberforce and said, “Unless God has raised you up for this very thing, you will be worn out by the opposition of man and devils. But if God be for you, who can be against you.” Two years later Wilberforce wrote in a letter, “I daily become more sensible that my work must be affected by constant and regular exertions rather than by sudden and violent ones.” In other words, with fifteen years to go in the first phase of the battle, he knew that only a marathon mentality, rather than a sprint mentality, would prevail in this cause.

–John Piper, Amazing Grace in the Life of William Wilberforce.