Here the flesh is not necessarily the physical body. In the Bible, the word “flesh ” is sometimes used to denote the sinful and imperfect nature of the fallen flesh.
يَتَحَدَّثُ بُولُسُ بَعْدَ ذلِكَ فِي رِسَالَتِهِ إِلَى أَهْلِ رُومَا عَنْ نَوْعَيْنِ مِنَ ٱلنَّاسِ فِكْرُ كُلٍّ مِنْهُمَا مُوَجَّهٌ بِعَكْسِ ٱلْآخَرِ .‏ ‏