Romans 6:11-12

Romans 6:11-12. Likewise reckon ye also yourselves to be dead indeed unto sin, but alive unto God through Jesus Christ our Lord. Let not sin therefore reign in your mortal body, that ye should obey it in the lusts thereof.

It is in the body that it tries to reign. These poor things, these mortal frames of ours, have so many passions, so many desires, so many weak-messes, all of which are apt to bring us under the dominion of sin, unless we watch with great care.