Discernment should not only be exercised with new ministers, but veterans as well. Our enthusiasm about a ministry may die down over time, or we may feel burned out; just a few reasons why discernment should be ongoing.
There are many things we can do to serve God, but not necessarily the one good thing God wants us to focus on. We're asked to do this and that. We run from one ministry to the next. Tuesday here, Sunday there. And who's laughing at us more than Satan!