Passage
If I say, Surely the darkness shall overwhelm me, And the light about me shall be night;
If I say, Surely the darkness shall overwhelm me, And the light about me shall be night;
Psalms 139:9 If I take the wings of the morning, And dwell in the uttermost parts of the sea;
Psalms 139:10 Even there shall thy hand lead me, And thy right hand shall hold me.
Psalms 139:11 If I say, Surely the darkness shall overwhelm me, And the light about me shall be night;
Psalms 139:12 Even the darkness hideth not from thee, But the night shineth as the day: The darkness and the light are both alike [to thee].
Psalms 139:13 For thou didst form my inward parts: Thou didst cover me in my mother`s womb.
The verse centers on "light", "darkness", "surely", "shall", "overwhelm", and "night". It is saying that the contrast between light and darkness marks a real divide in how people respond to God's work.
The nearby context moves from verse 10's "Even there shall thy hand lead me..." into verse 12's "Even the darkness hideth not from thee...", so "light" and "darkness" 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 "light" and "darkness" with trust shaped by these words, not by a vague optimism outside the passage.