Thou knowest my downsitting and mine uprising, thou understandest my thought afar off.
Afar off — Thou knowest what my thoughts will be in such and such circumstances, long before I know it, yea from all eternity.
 Thou compassest my path and my lying down, and art acquainted with all my ways.
Compassest — Thou discernest every step I take. It is a metaphor from soldiers besieging their enemies, and setting watches round about them.
 Thou hast beset me behind and before, and laid thine hand upon me.
Beset me — With thy all-seeing providence.
And laid — Thou keepest me, as it were with a strong hand, in thy sight and under thy power.
 Such knowledge is too wonderful for me; it is high, I cannot attain unto it.
I cannot — Apprehend in what manner thou dost so presently know all things.
 If I ascend up into heaven, thou art there: if I make my bed in hell, behold, thou art there.
Hell — If I could hide myself in the lowest parts of the earth.
 If I take the wings of the morning, and dwell in the uttermost parts of the sea;
The wings — If I should flee from east to west: for the sea being the western border of Canaan, is often put for the west in scripture. And wings are poetically ascribed to the morning here, as they are elsewhere to the sun, and to the winds.
 Thine eyes did see my substance, yet being unperfect; and in thy book all my members were written, which in continuance were fashioned, when as yet there was none of them.
Imperfect — When I was first conceived.
Book — In thy counsel and providence, by which thou didst contrive and effect this great work, according to that model which thou hadst appointed.
 How precious also are thy thoughts unto me, O God! how great is the sum of them!
Thoughts — Thy counsels on my behalf. Thou didst not only form me at first, but ever since my conception and birth, thy thoughts have been employed for me.
 If I should count them, they are more in number than the sand: when I awake, I am still with thee.
Them — Thy wonderful counsels and works on my behalf come constantly into my mind.
 I hate them with perfect hatred: I count them mine enemies.
Perfect hatred — See the difference between the Jewish and the Christian spirit!