its a quotation from Scripture ([Iyov 31:2]( 

and see tanya, (by rabbi shneur zalman boruchovitch - first lubavitch rebbe ) those are the first words of [chapter two:]( (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