The term "wicked" (Heb. rasa") usually describes people who do not have a covenant relationship with God. They have little regard for God but live to satisfy their passions. They are not necessarily as evil as they could be, but they have no regard for the spiritual dimension of life, so they are superficial. Chaff is the worthless husk around a head of grain that is light in weight and blows away in the winnowing process. It is neither admirable nor beneficial to others. [source][source][source]
Context Summary
Psalms 1:1-6 - The Two Ways And The Two Ends
Like a signpost, this psalm points the road to blessedness. The opening word may be read, "Oh, the blessedness!" The psalm begins with the same message as the Sermon on the Mount, Matthew 5:1-48. Beneath the lintel of benediction we pass into the temple of praise.
Blessedness is obtainable in two ways: negatively, we may avoid the society of the irreligious; positively, we must enter the company of prophets and kings, of psalmists and historians, and especially of God Himself, speaking in Scripture. Do not simply read the Bible; meditate upon it. Better one verse really masticated than a whole chapter bolted.
The rewards are, to be planted by rivers, to bear fruit, and to prosper. See Genesis 39:3-4; Genesis 49:22. How blessed it is, also, to realize that God knows and loves! See Psalms 56:8. The sinner begins with ungodliness, goes on to scorning, and ends as chaff, Matthew 13:30. [source]
Chapter Summary: Psalms 1
1The happiness of the godly 4The unhappiness of the ungodly
What do the individual words in Psalms 1:4 mean?
Notsothe ungodly [are]forbut[are] like the chaffwhichdrives awaythe wind