its a quotation from Scripture (Iyov 31:2)

and see tanya, (by rabbi shneur zalman shneurson - 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