That other force is what the Scriptures term “the flesh, ” which refers to the sinful inclinations of our fallen flesh, the legacy of imperfection we have received as descendants of Adam.
لِأَنَّ ثَمَّةَ قُوَّةً أُخْرَى مُقَاوِمَةً لِعَمَلِهِ تَسْعَى إِلَى ٱلسَّيْطَرَةِ عَلَيْنَا .‏