Thou compassest my path and my lying down,.... 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 word ; 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" ; all his dimensions, his length and breadth, as he lay down in his bed;and art acquainted [with] all my ways; the whole of his life and conversation, all his works and doings: God knows all the evil ways and works of his people; he takes notice of them, and chastises for them; and all their good works, and approves and accepts of them; he knows from what principles of faith and love they spring, in what manner they are performed, and with what views, aims, and ends; see Re 2:2 Ps 1:6.
tyrz "ventilasti", Pagninus, Montanus; so Tigurine version and Ainsworth. yebr "quadraturam meam spithama mensurasti", Gussetius, p. 775.