Behold, thou hast made my days as an handbreadth; and mine age is as nothing before thee: verily every man at his best state is altogether vanity. Selah.
And mine age (note, 'the world'-same Hebrew as "age" - Psalms 17:14)
Is as nothing before thee - `is as non-existence' (Hengstenberg). "Before thee:" this appointment proceeds from thee.
Verily every man at his best state is altogether vanity - Hebrew, 'only all vanity is every man constituted' х nitsaab (H5324)]. Constituted (by the Creator) answers to the previous "thou hast made," and "before thee;" i:e., by thine appointment. All men are constituted as only an all of vanity.
Selah - giving time for a pause (as Selah means) to meditate over the mournful nothingness of life.