What has happened to Christendom in general according to Les?
Christendom in general has been leavened. Christianity today is leavened, because false teaching acts like yeast and permeates the whole lump. Consequently, the things Scripture and Christianity stood against fifty, sixty, or seventy years ago are now part and parcel of everyday experience, and the church can no longer be distinguished from the world.
Les explains that leaven is yeast, and when yeast is put into dough it does not leaven just a fourth of it but the whole lump. In the same way, if a little false teaching is allowed in as leaven, it is not long until it permeates the whole, and one thing leads to another. He then asks what has happened to Christendom in general and answers that it has been leavened, and Christianity today is leavened. All the things Scripture and Christianity stood against fifty, sixty, or seventy years ago are now part and parcel of everyday experience. He illustrates this with a church he visited when one of his children was at the university: the pastor made a tremendous point that all the things of the world came knocking on the church's door, and the church said it could accommodate that and live with it. Then the door opened a little further, some other world stuff came in, and the church again said it could live with that. Now the doors are wide open, and you cannot tell the difference between the church and the world. The summary is that a little leaven leavened the whole lump.
A little leaven leaveneth the whole lump.