its a quotation from Scripture (Iyov 31:2) http://www.biblegateway.com/passage/?search=Iyov+31%3A2&version=OJB
and see tanya, (by rabbi shneur zalman shneurson - first lubavitch rebbe ) those are the first words of chapter two: http://www.chabad.org/library/tanya/tanya_cdo/aid/7881/jewish/Chapter-2.htm, (with the addition of the word "mamesh" ) it is explained there a length.
here is a quote
to describe G-d’s implanting the Jew’s soul in his body signifies that this soul originates in the “innermost” aspect of G-dliness.
see there at length