“One important thing to bear in mind, in all this, is that the Buddha’s mercy is providential, but does not, for this very reason, suspend the Law of Karma: if beings will persist in ignoring that law while coveting the things mercy might have granted them, that mercy itself will reach them in the guise of severity; severity is merciful when this is the only means of provoking a radical metanoia (change of outlook), failing which wandering in samsâra must needs continue indefinitely. The nembutsu is our ever-present reminder of this truth; if, in reliance on the Vow, we abandon all wish to attribute victory to ourselves, the unfed ego will surely waste away, leaving us in peace.”
(Marco Pallis, Nembutsu as Remembrance; http://studiesincomparativereligion.com/public/articles/Nembutsu_as_Remembrance-by_Marco_Pallis.aspx)