Mourn
In a general sense, mourning in the Bible represents a state of grief over the lack of desires for good and true ideas about life. This often happens when a church or an aspect of a church has fallen away from the Lord and has been devastated. It can also be when a new church or state of a church is soon to begin, and there is nothing yet in place. In particular, especially when paired with "weeping," "mourning" has do with the loss of all desire for good and the presence of evil; "weeping" in those cases has to do with the devastation of thought and knowledge.
Arcana Coelestia #860
860. From these considerations it also becomes clear that all regeneration advances from evening to morning, as is mentioned six times in Genesis 1 where the regeneration of man is the subject. Here the evening is described in verses 2-3, the morning in verses 4-5. The present verse describes the first ray of light or the morning of this state as 'the tops of the mountains appearing'.