He uses the illustration of pole vaulters. If the bar is set at six feet above the ground, most apprentice pole vaulters can clear it easily. Raise the bar three or four feet and that will separate the skilled from the unskilled. Raise the bar to twelve feet and you will separate the committed from the wannabees. The mediocre pole vaulters can clear nine feet, but not fourteen feet.
New generations keep raising the bar.
They bring a higher set of expectations. A hundred years ago, the younger generations began to expect the building should and would be heated on a cold winter morning. Seventy years ago, the younger generations began to expect indoor plumbing. Forty years ago, younger generations began to expect a convenient parking place. Thirty years ago, they began to expect the churches would provide an attractive, soundproof and comfortable room for each Sunday School class.