A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
psa 39:1To Jeduthun (Ch1 16:41-42), one of the chief singers. His name mentioned, perhaps, as a special honor. Under depressing views of his frailty and the prosperity of the wicked, the Psalmist, tempted to murmur, checks the expression of his feelings, till, led to regard his case aright, he prays for a proper view of his condition and for the divine compassion. (Psa 39:1-13)
I said--or, "resolved."
will take heed--watch.
ways--conduct, of which the use of the tongue is a part (Jam 1:26).
bridle--literally, "muzzle for my mouth" (compare Deu 25:4).
while . . . before me--in beholding their prosperity (Psa 37:10, Psa 37:36).
psa 39:2even from good-- (Gen 31:24), everything.
psa 39:3His emotions, as a smothered flame, burst forth.
psa 39:4Some take these words as those of fretting, but they are not essentially such. The tinge of discontent arises from the character of his suppressed emotions. But, addressing God, they are softened and subdued.
make me to know mine end--experimentally appreciate.
how frail I am--literally, "when I shall cease."
psa 39:5His prayer is answered in his obtaining an impressive view of the vanity of the life of all men, and their transient state. Their pomp is a mere image, and their wealth is gathered they know not for whom.
psa 39:7The interrogation makes the implied negative stronger. Though this world offers nothing to our expectation, God is worthy of all confidence.
psa 39:8Patiently submissive, he prays for the removal of his chastisement, and that he may not be a reproach.
psa 39:11From his own case, he argues to that of all, that the destruction of man's enjoyments is ascribable to sin.
psa 39:12Consonant with the tenor of the Psalm, he prays for God's compassionate regard to him as a stranger here; and that, as such was the condition of his fathers, so, like them, he may be cheered instead of being bound under wrath and chastened in displeasure.