Increases spirit regeneration by X per second
They constantly regenerate spirit when you're standing idle (in other words, increase passive spirit regeneration), similar to the Chant of Resonance passive.
As far as I know, the only way to increase the rate of spirit generated by spirit generators across the board is to use a 2-hander and The Guardian's Path passive.
They give you X spirit per second. For example if you have a total of 5 increased spirit regenerated per second, then each second you will generate 5 spirit at all times, in addition to any other spirit generating ability you use.