To the chief Musician. See App-64. The changes from 2Samuel 22 were made when David handed the Psalm over for general use in public worship. The position of this Psalm in the Structure (p. 721) shows that it corresponds with, Psa 29, with its two answering parts, the "Glory" and the "Voice" of Jehovah. The verbs in the first part (1-6) are literary, and in the second part astronomical, thus interlacing and uniting the two parts in one whole.
Title. A Psalm of David. One Psalm: one whole, not two odd scraps strung together by some late "redactor". See App-65.
declare = rehearse (the Piel part, implying repetition. Compare Psa_71:15. Gen_24:66. Figure of speech Prosopopoeia.App-6.
GOD. Hebrew El. App-4.
firmament = expanse.
sheweth = is setting forth. Compare first occurrence (Gen_3:11. Psa_97:6; Psa_111:6).