dust. Figure of speech Metonymy (of Cause), App-6, put for the body which is made of dust (Genesis 2:7; Genesis 3:19; Psalms 104:29; Job 34:15; Job 34:16).
as it was. Note the reference to Adam's creation.
spirit. Hebrew. ruach. App-9. Not nephesh, soul (App-13).
return unto God. Hence He is said to be the God of the spirits of all flesh (Numbers 16:22; Numbers 27:16. Compare Luke 23:46; Acts 7:59); "the Father of spirits" (Hebrews 12:9).
God. Hebrew. Elohim. (with Art.). the (true or triune) God; the Deity. App-4. Concerning where the dead are, for us to assume any further than what is said here (Ecclesiastes 12:7) is no more than mere speculation.