Joy Nugget #8: Commands to Mourn?

Just as there are commands to rejoice, there are also commands to mourn:

-Jeremiah's soul is in anguish as he learns of a severe desolation where the whole earth will mourn.
-The priests are told to mourn because the sacrifices have been cut off from the house of the Lord (Joel 1:9-13 and 2:17)
-The Spirit of God will cause the people to mourn bitterly for the One they have pierced (Zechariah 12:10-14)
-Mourning is appropriate when the "bridegroom" (Christ) is 'away'. (Matthew 9:15)
-We are commanded to "rejoice with those who rejoice" and "weep with those who weep". (Romans 12:15)

So which is it? Rejoice and mourn too?