The ‘rich’ he’s talking about here are those who become wealthy by ungodly means and live ungodly lives.  Verse 4 talks about wages being withheld by the rich from those who work in their fields.  Verse 5 talks about living in pleasure.  The Amplified Bible says "self indulgence and self-gratification."  And verse 6 says they have condemned and put to death the righteous man.

He’s calling for those who live this way to ‘weep and howl’ (The Amplified says "weep aloud and lament"), over the miseries which are coming upon them.  In other words, he’s calling for them to mourn and repent over their sin otherwise miseries will come upon them.

Sometimes it may appear that people are ‘getting away’ with living a cruel and ungodly life but it will catch up to them.  They will reap what they sow.  We need to remember that and not be bitter in our hearts against those types of people (And we need to be sure we are not of ‘those people’).  We need to call for repentance and our desire and prayers should be for them to repent and receive mercy.

Confession:

I realize those who live cruel and ungodly lives will reap what they sow.  They’ll not get away with living that way unless they have true repentance and receive mercy from God.  I desire repentance and mercy for them and will not be bitter against them.  If I have been one of "them" I repent and ask for forgiveness now in the Name of Jesus.