[Tuidjy]

The hammer does not increase the magic level. It lets you forge items with fewer
gems. The item that will increase your Earth magic level is the pair of boots that
you can forge with 10 earth gems at Construction level 4. With the hammer, it will
take you only 7 earth gems.

For an example of using the thistle mace - you have a druid with nature level one.
Give him the thistle mace, and now his magic level is two. He could cast, every
turn, the spell "Haruspex", and he would discover all nature sites (if any) in the
targeted province. Or in combat, instead of casting:
Eagle Eyes, Vine Arrow, Vine Arrow, Vine Arrow, Vine Arrow, etc..
he could be casting
Eagle Eyes, Storm of Thorns, Storm of Thorns, Storm of Thorns, Storm of Thorns, etc...
which not only has higher range, but also half a dozen extra projectiles.

Of course, the above example is very simple... but to get really good, the best way
is to jump in a MP game, and when your favorite army gets wiped out by something
that does not break a sweat, learn.