He does so by,
a. Giving the seeker hope. That is, it is human to err and Allah is Most Merciful to those who acknowledge their short comings.
b. Instruction to forget the past. Bury it. If this is not done, its dead body will rot and the stench emanating from it will spoil the best aroma of sincere good acts done in future. Also, remembering the sins after sincere repentance is wrong and leads to decreasing relationship with Allah.
c. To be concerned with improving the present condition right now. For this today will tomorrow become yesterday. A thing of past.
If handled in this way each and every mistake and fall of the sincere seeker results in increasing relationship with Allah, enhanced humility and complete dependence on His kindness and mercy.
A seeker should remember that these falling episodes are not uncommon and continue until a permanent spiritual serenity (tamkeen) is achieved (which usually happens after years of sincere effort by method described above). Until then he/she has to bury the past with sincere repentance and move forwards on the path with renewed vigor.
And its facilitation is surely from Allah, Most High.
(Courtesy of Ashrafiya)