Deriving a novel argument for God's existence and producing a new treatment of central mysteries of the Christian faith are significant achievements in their own rights, befitting their author a place in pantheons of philosophy and theology. But, there is yet more, much more, than even these in Anselm's work. Another set of achievements are hinted at early on in Cur Deus Homo, where Anselm attempts to beg off the task his student lays upon him:
. . . .we need an analysis of ability and necessity and will and of certain other notions which are so interrelated that no one of them can be fully examined apart from the others. And so, to deal with these notions requires a separate work — one not very easy [to compose], it seems to me, but nonetheless one not altogether useless. For an ignorance of these notions produces certain difficulties which become easy [to deal with] as a result of understanding these notions.
[using, as is my wont in these blogs, Hopkins and Richardson's translations,]