I call to remembrance my song in the night - I do not think that נגינתי neginathi means my song. We know that נגינת neginath signifies some stringed musical instrument that was struck with a plectrum, but here it possibly might be applied to the Psalm that was played on it. But it appears to me rather that the psalmist here speaks of the circumstances of composing the short ode contained in the seventh, eighth, and ninth verses; which it is probable he sung to his harp as a kind of dirge, if indeed he had a harp in that distressful captivity.
My spirit made diligent search - The verb חפש chaphas signifies such an investigation as a man makes who is obliged to strip himself in order to do it; or, to lift up coverings, to search fold by fold, or in our phrase, to leave no stone unturned. The Vulgate translates: "Et scopebam spiritum meum." As scopebam is no pure Latin word, it may probably be taken from the Greek σκοπεω scopeo, "to look about, to consider attentively." It is however used by no author but St. Jerome; and by him only here and in Isaiah 14:23; : And I will sweep it with the besom of destruction; scopabo eam in scopa terens. Hence we see that he has formed a verb from a noun scope, a sweeping brush or besom; and this sense my old Psalter follows in this place, translating the passage thus: And I sweped my gast: which is thus paraphrased: "And swa I sweped my gaste, (I swept my soul), that is, I purged it of all fylth."
I call to remembrance my song in the night - Compare Job 35:10, note; Psalm 42:8, note. The word here rendered “song” - נגינה negı̂ynâh - means properly the music of stringed instruments, Lamentations 5:14; Isaiah 38:20; then, a stringed instrument. It is the word which we have so often in the titles to the psalms (Psalm 4:1-8; Psalm 6:1-10; Psalm 54:1-7; Psalm 67:1-7; Psalm 76:1-12); and it is used here in the sense of song or psalm. The idea is, that there had been times in his life when, even in darkness and sorrow, he could sing; when he could find things for which to praise God; when he could find something that would cheer him; when he could take some bright views of God adapted to calm down his feelings, and to give peace to his soul. He recalls those times and scenes to his remembrance, with a desire to have those cheerful impressions renewed; and he asks himself what it was which then comforted and sustained him. He endeavors to bring those things back again, for if he found comfort then, he thinks that he might find comfort from the same considerations now.
I commune with mine own heart - I think over the matter. See the notes at Psalm 4:4.
And my spirit made diligent search - In reference
(a) to the grounds of my former support and comfort; and
(b) in reference to the whole matter as it lies before me now.