Did Jesus die in vain if fewer people are saved than we expect?
No, Jesus did not die in vain. Although the number of saved people will be fewer than many expect, every believer is His for eternity. The multitude who have become believers belong to Him, and no one can ever take them from Him. His death accomplished its purpose.
Les teaches that Christ did not die in vain. He explains that God's promise to Abraham was that everyone who puts their trust in what He accomplished would be His for all eternity. While Les acknowledges that God will not get near as many as we think He should, the multitude who have become believers are His, and no one can ever take them from Him. This connects to the allegory of Isaac and Ishmael: the desolate woman has many more children than she who has a husband, and in the real world Ishmael's offspring (the Arab world) outnumber Isaac's (the Jews) 50 to 1. Yet the promise remains secure for all believers.
Now we, brethren, as Isaac was, are the children of promise.