One of the first things the Rebbe Rashab taught his son and future Rebbe the friedikeh Rebbe (the previous Rebbe) was the teaching of the Alter Rebbe that as the redemption from Egypt was a revelation, it needed only 210 years preparation, (for, to say, be worthy to see a great show, you may need to pay a lot) but as this future redemption is not a revelation, rather it is the merging of the Divine essence within humanity (and like the difference between seeing, say, a beloved artist performing on stage, versus the amount of effort to woo and marry and then remain eternally in love!) hence the inordinate preparation for the current redemption.