I shall stretch

Psalm 78:33
brought
futility
their days
and their years
sudden

Genesis 2:1
were completed*
the heaven
and the earth
and all
their hosts

Genesis 2:2
completed
god
day
the seventh
his work
which
had done
rested
day
the seventh
all
his
work
which
had
done

My theory (it is a stretch) is the word for "completed" carries the idea that the thing completed is not finished, but has entered another stage of making.  So the seventh day is a HOPING for rest.  One way or another The God will find rest on the seventh day.
How?  I'm glad you asked!
I looked up "completed" the word for what the writer described God doing and found that the word is used in the Old Testament for something someone had to come to an end of (like a speech, or a life) but carried with it expectation of something that should follow.

*this word for completed is used only once in the Old Testament.

http://concordances.org/hebrew/vaychal_3615.htm