Did being part of Israel under Abraham's root make every Jew a believer?
No, being under Abraham’s root did not make every Jew a believer. Most Israelites were not believers, even though they rested on the root and fatness of Abraham. That position gave them privilege and opportunity, not automatic salvation. The same principle applies to Gentiles: they have opportunity and responsibility, but salvation requires appropriating it by faith like Abraham’s.
Les explains that Israel was resting on the root and fatness of the man of faith Abraham, but that did not automatically make every Jew a believer. Most of them were not. He then applies the same principle to Gentiles: as Gentile nations, they are now in a place of privilege, blessing, and opportunity to hear the Gospel and be saved, but that does not mean every Gentile will be saved. Every Gentile has opportunity and will be held responsible at the great white throne; they cannot say they never had a chance. Les stresses that when Christ died, He took care of all sins, and every human being has already been declared reconciled and pardoned so far as God is concerned. But until they appropriate it with the kind of faith Abraham had, which was relatively simple, it is all for nothing. God does not look for someone who knows the Bible from cover to cover or for a primary example of holy living before He can save.