Catechism 15

Since no one can keep the law, what is its purpose?
That we may know the holy nature and will of God, and the sinful nature and disobedience of our hearts; and thus our need of a Savior. The law also teaches and exhorts us to live a life worthy of our Savior.
(New City Catechism)

So earthly good starves, yet Law stands,
a good tree planted in sick soil,
exemplar of life, arrow to Eden.

And we, though our stomachs
sicken at the sight, may eat –
if we first learn to kneel at its roots.

Desperation must come first: the cry 
of a helpless heart eternally lost,
mercy the one last, half-hoping hope.

Then the tree: planted in the place of skulls,
and the Exemplar ascending,
desperate and hopeful, merciful to the last.