Psalms 139:3

“Thou compassest my path and my lying down, etc.] The Targum adds, “to study in the law.” His walk in the daytime, and every step he took, and his lying down at night. It denotes his perfect knowledge of all his actions, day and night; he surrounds every path of man, that they cannot escape his knowledge. Or, “thou winnowest”, as some render the wordf1847; he distinguishes actions; he discerns and separates the good from the bad, or the goodness of an action from the evil and imperfection of it, as in winnowing the wheat is separated from the chaff. Or, “thou measurest my squaring”f1848; all his dimensions, his length and breadth, as he lay down in his bed; and art acquainted [with] all my…”

“Thou compassest my path ... - Margin, “winnowest.” The Hebrew word - זרה zârâh - means properly “to scatter,” to cast loosely about - as the wind does dust; and then, to winnow - to wit, by throwing grain, when it is thrashed, up to the wind: Isaiah 30:24; Jeremiah 4:11; Ruth 3:2. Then it means “to winnow out;” that is, to winnow out all the chaff, and to leave all the grain - to save all that is valuable. So here it means that God, as it were, “sifted” him. Compare Isaiah 30:28; Amos 9:9; Luke 22:31. He scattered all that was chaff, or all that was valueless, and saw what there was that was real and substantial. When it is said that he did this in his “path and his lying down,” it is…”

“Compassest - Thou discernest every step I take. It is a metaphor from soldiers besieging their enemies, and setting watches round about them. Psalms 139:5”

“139:3-6 The Lord’s omniscience and omnipotence provide comfort to the godly, but they imprison the hearts of the wicked (2:3).”

“compassest: or, winnowest, Job 13:26, Job 13:27, Job 14:16, Job 14:17, Job 31:4; Mat 3:12 my path: Psa 139:18, Psa 121:3-8; Gen 28:10-17; Sa2 8:14, Sa2 11:2-5, Sa2 11:27 and art acquainted: Sa2 12:9-12; Pro 5:20, Pro 5:21; Ecc 12:14; Isa 29:15; Jer 23:24; Joh 6:70, Joh 6:71, Joh 13:2, Joh 13:21; Act 5:3, Act 5:4 Psalms 139:4”