Charles Ellicott Commentary Jeremiah 17:8

"For he shall be as a tree planted by the waters, that spreadeth out its roots by the river, and shall not fear when heat cometh, but its leaf shall be green; and shall not be careful in the year of drought, neither shall cease from yielding fruit." — Jeremiah 17:8 (ASV)

Shall not see when heat cometh. —Another reading, followed by the Septuagint and Vulgate, gives shall not fear; there is, however, more force in the repetition of the same word as in Jeremiah 17:6.

The man who trusts is like the strong tree, clothed with foliage, that “does not see,” i.e., does not regard or feel, the presence of the heat. Technically the meaning is the same in both cases, but in the latter case with the emphasized contrast of a parallelism.

Fed by the stream that never fails, it shall not be careful or anxious about the scorching heat of summer. As the blasted heath sees no good, so the tree, in this case, sees no evil.