Whoever has faith in individual Divine Providence knows that "Man's steps are established by G-d" (Psalms 37:23)--that this particular soul must purify and improve something specific in a particular place. For centuries, or even since the world's creation, that which needs purification or improvement waits for this soul to come and purify or improve it. The soul too, has been waiting - ever since it came into being - for its time to descend, so that it can discharge the tasks of purification and improvement assigned to it.