You, O LORD, will keep them; you will guard us from this generation forever. On every side the wicked prowl, as vileness is exalted among the children of man.
God's activity in our lives is protective and secures us from the wicked influences that surround us. It is one reason why we call out to Him. In this Psalm the main complaint is that the poor tend to be trampled by evil men. There is a preference among men to exploit the poor. But there is an action by God to protect them. And this Psalm cries out for that to be what God does.
The faith of this prayer is bound up in the convictions that 1) God will keep the poor. He protects them and 2) God will act against those who seek to exploit others. He will guard by protecting and by proactively judging the wicked acts of those who exploit them.
The image of the ever present danger of evil is frightening in verse eight. Wickedness is predatory. It prowls about looking to victimize the weakest members of a society. And wickedness is self-congratulatory. It likes to celebrate its wrongs. And people will enjoy the party... for a short while.
That is why the prayer for God to act is so important. It helps righteous people maintain perspective. And God will work against the wicked who hurt others. Sadly, it is a prayer I do not pray enough, for if I did, I'd act on it at God's moving.