Why did God insert the Church Age between the first and second coming?
The Church Age was inserted because Israel rejected the King and Kingdom at His first coming, so prophecy did not flow directly into the Kingdom Age. This parenthetical period, unknown to Old Testament writers, was opened up for Gentile believers and was not revealed in Old Testament prophecy.
Les teaches that all prophecy was directed to the nation of Israel, and no prophecy gives any indication of the Church as such. Not a word is breathed throughout the Old Testament about this Church Age comprised of Gentile believers. The Old Testament prophets understood there was something between His first advent and His coming in power and glory, but they viewed the two advents like distant mountain ranges that looked like one range; they could not discern the valley in between. According to prophecy, it was supposed to go beyond the cross, Israel would have her King and the Kingdom, and they would go into the Kingdom Age. But it did not end that way because Israel rejected it, and unknown to the Old Testament writers, that whole period of time was opened up and parenthesized, which we call the Church Age.