The gemara in Shabbos (118b) says that had Bnei Yisroel kept the first Shabbos in the Midbar they would have become invincible. However the Mikoshesh spoiled that by being Michalel Shabbos. The next gemara says that if we keep two Shabbosos we would be immediately redeemed. So do we need one Shabbos or two, and why is this?
Rav Eliyahu Dessler in michtav MeiEliyahu says that the gemara is not referring to two Shabbosos on the calendar but rather two aspects of Shabbos. Using this approach maybe we could answer as follows. The gemara tells us that speaking Divrei Chol on Shabbos is forbidden, yet thinking it is permitted. On the other hand Chazal tell us that on Shabbos we should view our work, K'Ilu Milachticha Asuya, as if it is all wrapped up and there is nothing left to be taken care of. Shabbos should be free from all thoughts of work and should be treated like a utopia.
Shabbos is a day of MeiEin Olam Haba. It is the purpose of the six days of creation. Similarly the world is for six thousand years and the seventh thousand years is Shabbos. By keeping Shabbos and totally removing ourselves from the mundane aspects of the world we are in a state of Geula. We have reached perfection. Once we accomplish that, surely Hashem will effect the final Geula and our state will continue.
In the Midbar, Bnei Yisroel lived everyday as if there were no tomorrow. Keeping Shabbos entailed not doing any Milacha. Had Bnei Yisroel accomplished that they would have reached perfection. We on the other hand do better with the actual refraining from Milacha, whereas we are still far from perfecting our spiritual understanding of Shabbos. Once we learn how to keep both these Shabbosos, Hashem will immediately redeem us.