When G-d informed Moses that he would not merit to enter the land of Israel, Moses prayed repeatedly to G-d to rescind the decree: "And I beseeched G-d... please let me cross over and see the land." According to our sages, Moses prayed a total of 515 times, the numerical value of the word Vaetchanan (and I beseeched).
What lesson do we take from this? Can anything positive come out of knowing that Moses himself prayed for something 515 times and was ultimately refused?
It cannot be that the prayers of Moses were in vain. Without doubt, they accomplished their purpose in the heavenly realms. If our ancestors had merited it, these prayers would have been fulfilled in actuality and Moses would have led them into the land. However, for various reasons, the prayers remained in heaven, and Moses was buried in the desert. Yet those prayers are still kept in reserve, and will ultimately be fulfilled in the time of the final Redemption.
We learn from Moses how strong our longing must be for the Redemption. Moses heard explicitly from G-d that he would not merit the Redemption, yet he did not cease his prayers for the nullification of the decree, even after G-d asked him to stop. We have not been asked to stop; we must continue our prayers without interruption, until we merit the final Redemption.