Or, “He hath” made me to dwell “in darkness,” i. e. in Sheol or Hades, “as those” forever “dead.”
Matthew Henry
Concise Bible Commentary
The prophet relates the more gloomy and discouraging part of his experience, and how he found support and relief. In the time of his trial the Lord had become terrible to him. It was an affliction that was misery itself; for sin makes the cup of affliction a bitter cup. The struggle between unbelief and faith is often very severe. But the weakest believer is wrong, if he thinks that his strength and hope are perished from the Lord.
SDA Bible Commentary (limited)
Volume 1-7
6. He hath set. In the Hebrew Bible, this verse is almost identical with the last part of Ps. 143:3. Its appearance here is indicative of Jeremiah’s familiarity with the psalms.
Dark places. This testifies to the truth that the resting place of the dead is one of darkness and inactivity (see on Eccl. 9:10; Isa. 38:18).