The imagery of the "rod of the wicked" "resting" upon the righteous is a terrifying one. It implies unrelenting, unrelieved oppression. But God has promised that the wicked will not have a continuous unending victory over good people. Of course, there may be moments -- long moments-- when it looks as if evil has actually found a home in our lives. But God is aware that good people can be tempted to turn to evil if they feel overwhelmed by life's troubles. This is the same sentiment expressed in Proverbs 30:8,9. God understands that hopelessness can make even a good person turn to evil. It is also expressed in Psalm 37:1,2, where the believer in God is warned not to fret themselves because of the evil and injustice they see in the world.
Thus the psalmist then reminds God to do good to good people. It is a good thing to remind God and one's self of His mercy. Yet, even if Gods mercy seems delayed, the righteous person should not feel he has an excuse to turn from righteousness. As the psalmist reminds his readers, God will punish the backslider and the evil person together.
1They that trust in the LORD shall be as mount Zion, which cannot be removed, but abideth for ever.
2As the mountains are round about Jerusalem, so the LORD is round about his people from henceforth even for ever.
3For the rod of the wicked shall not rest upon the lot of the righteous; lest the righteous put forth their hands unto iniquity.
4Do good, O LORD, unto those that be good, and to them that are upright in their hearts.
5As for such as turn aside unto their crooked ways, the LORD shall lead them forth with the workers of iniquity: but peace shall be upon Israel.