Passage
Dost Thou slay, O God, the wicked? Then, men of blood, turn aside from me!
Dost Thou slay, O God, the wicked? Then, men of blood, turn aside from me!
Psalms 139:17 And to me how precious have been Thy thoughts, O God, how great hath been their sum!
Psalms 139:18 I recount them! than the sand they are more, I have waked, and I am still with Thee.
Psalms 139:19 Dost Thou slay, O God, the wicked? Then, men of blood, turn aside from me!
Psalms 139:20 Who exchange Thee for wickedness, Lifted up to vanity <FI>are<Fi> Thine enemies.
Psalms 139:21 Do not I hate, Jehovah, those hating Thee? And with Thy withstanders grieve myself?
The verse centers on "dost", "thou", "slay", "wicked", "blood", "turn", and "aside". It is saying that the verse draws attention to "dost" and "thou", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 18's "I recount them than the sand they..." into verse 20's "Who exchange Thee for wickedness Lifted up...", so "dost" and "thou" belong inside that flow. In Psalms context, the local focus is worship, trust, the LORD's kingship, and covenant mercy.
A plain takeaway is to answer the verse's own emphasis on "dost" and "thou" with trust shaped by these words, not by a vague optimism outside the passage.