When a church is falling and loses its desire for good, those within it who desire what is good will grieve. That's the state represented by "mourning" in the Bible. On a personal scale this also happens inside us as we move from lower spiritual states to higher ones. To be "comforted" represents an influx of new ideas which can help us move on to a new spiritual state or – on the wider scale – can help rejuvenate or even replace the church.

Here, then, we see the Lord promising the good people of the Jewish church - the ones grieving over its fallen state and the self-serving ways of its leaders – that they would receive ideas that would let them move on to the new church he was establishing in the world.

Feelings of joy and rejoicing flow from our affections, not from our thoughts. Some people might argue that that's not true, that you can rejoice over learning a new idea or having a new thought -- but really you're rejoicing because you have an affection for that idea, or even simply an affection for growing wise (something very strong in men in particular). So when the Bible talks about rejoicing, exulting, or feeling joy, it is talking about an excitement of the affections -- either good or evil. Often the Bible offers this idea in pairings -- "exult and rejoice," for instance, or "rejoice and be glad." Generally this means that the spiritual event is stirring both the affection we have for truth, for thoughts, and the affection we have for doing what is good.