What does the Bible say about the spirit and the flesh?

In Matthew 26:41, Jesus states, 'The spirit indeed is willing, but the flesh is weak.' This passage illustrates the struggle between the desires of the spirit and the inherent weakness of the flesh. Paul expands on this in Romans 7, where he describes the internal conflict faced by every believer: 'For to will is present with me, but how to perform that which is good, I find not' (Romans 7:18). This struggle reveals that while the believer's spirit yearns for holiness, the fallen flesh cannot help but succumb to sin, illustrating the concept of total depravity.