NanaR....Rutherford introduced the Jonadab class and relocated the "great multitude" to the earth in order to fix certain theological problems. He taught in the 1920s a new teaching about the "remnant", which claimed that the number of the elect would continue to decrease until Armageddon. This was another "fix", aimed at rationalizing the immense decrease in the movement on account of the 1925 failure and Rutherford's new teachings. Thus, the dramatic decrease was to be expected. But then the trends reversed in 1930 and 1931 because of the Great Depression.... new people started to enter into the movement in droves on account of the terible conditions at the time. So Rutherford had to explain why there was an increase. Hence, he invented a new class, the "Jonadabs" who associate themselves with the organization. But to maintain the pre-existing "remnant" teaching, Rutherford told them that they were an earthly class and not a member of either of the heavenly classes. This would prevent them from increasing the number of the Church, which was supposed to be declining.
But he knew that zealous neophytes could still decide that they were spirit-begotten, and with increased maturity over time claim that they are really members of the elect 144,000. He also needed to keep coming up with excuses to keep the Witnesses working hard for him (earlier excuses...1920-1921: Elisha work, mid-1920s: Vindication teaching). He solved both problems in 1935 by identifying the "great multitude" with the "Jonadab" class. Eliminating the older "secondary spiritual class" meant that a neophyte would have to claim to be of the elect 144,000 to assert a heavenly destiny (rather than a wider class of those with less spiritual maturity). It also allowed him to introduce a huge new field of work for the JWs, for the number of "Jonadabs" was still small and yet Revelation claimed that the "great multitude" was so vast no man could number it. This meant that the "gathering of the great multitude" must begin, and this dominated the preaching work from 1935 onward. And if the work was supposed to be focused on gathering the great multitude, then Rutherford could claim that the gathering of the elect has ended. This would also insure that the number would not increase and that the remnant teaching would not be contradicted by actual facts.
But his plan did not exactly work as well as he hoped. The gathering of the "great crowd" has indeed been the focus of the Society ever since, and this teaching has certainly been a great success. But there were still new people claiming to be members of the 144,000, and these were mostly of "Jonadabs" later deciding that they were really of the elect. This was officially rationalized as "replacements" for unfaithful elect....but the Society has strongly discouraged the practice and even hinted that those who decide they really have a heavenly hope are spiritually or mentally unstable. The "remnant" taeching meanwhile has been an abyssmal failure. Not only has the decrease that was so dramatic in the 1920s (now a distant memory) ground to a halt, but in many years the numbers actually increase.
I'm not sure how he was able to convince all the existing members of the "secondary spiritual class" that they have an earthly rather than a heavenly destiny, other than that he was the mouthpiece of Jehovah and reported Jehovah's "lighnings," as he puts it, so if he said so, I think most went along with him. Also, I think the number of the JWs considered of the "great multitude" had actually declined by this time. This group was as hard hit by the decreases of the 1920s as the elect, and the "Jonadab" teaching introduced in 1931 prevented many new members from joining the ranks of the secondary spiritual class, which is where neophytes would have gone previously.
