“Tremble and sin not.” How many reverse this counsel and sin but tremble not. O that men would take the advice of this verse and commune with their own hearts. Surely a thinking man might have enough sense to discover the vanity of sin and the worthlessness of the world. Stay, rash sinner, stay ere thou take the last leap. Go to thy bed and think-upon thy ways. Ask counsel of thy pillow, and let the quietude of night instruct thee! Throw not away thy soul for nought! Let reason speak! Let the clamorous world be still awhile, and let thy poor soul plead with thee to bethink thyself before thou seal its fate, and ruin it for ever!~ C. H. Spurgeon
'He warns them against sin, and exhorts them both to frighten and to reason themselves out of it.
Note, (1.) We must not sin, must not miss our way and so miss our aim. (2.) One good remedy against sin is to stand in awe. Be moved (so some), in opposition to carelessness and carnal security. "Always keep up a holy reverence of the glory and majesty of God, and a holy dread of his wrath and curse, and dare not to provoke him." (3.) One good means of preventing sin, and preserving a holy awe, is to be frequent and serious in communing with our own hearts: "Talk with your hearts; you have a great deal to say to them; they may be spoken with at any time; let it not be unsaid." A thinking man is in a fair way to be a wise and a good man.
"Commune with your hearts; examine them by serious self-reflection, that you may acquaint yourselves with them and amend what is amiss in them; employ them in solemn pious meditations; let your thoughts fasten upon that which is good and keep closely to it. Consider your ways, and observe the directions here given in order to the doing of this work well and to good purpose."
"Choose a solitary time; do it when you lie awake upon your beds. Before you turn yourself to go to sleep at night" (as some of the heathen moralists have directed) "examine your consciences with respect to what you have done that day, particularly what you have done amiss, that you may repent of it. When you awake in the night meditate upon God, and the things that belong to your peace." David himself practised what he here counsels others to do (Psa. 63:6).' ~ Matthew Henry
Stand in awe, and sin not,.... 'That is, stand in awe of God, and his righteous, judgments; be afraid of him, and tremble before him; make him your fear and your dread, and go on no longer and proceed no further in sinning against him'. ~ John Gill
And be still -
'When you are thus quiet, reflect on your doings. For a most beautiful description of the effect of night and silence in recalling wicked men from their schemes, see Job 33:14-17. Compare the notes at that passage.Selah -
This, as explained in the notes at Psalm 3:2, marks a musical pause. The pause here would well accord with the sense, and would most happily occur after the allusion to the quiet communion on the bed, and the exhortation to be still.' ~ Albert Barnes