The flesh - a Christian perspective
It's easy to want to do good and resist temptation, but it's hard to actually do it! This verse speaks of the difficulty of keeping our natural impulse toward sin under control.
The flesh is weak - a Christian perspective
Have you ever really wanted to avoid a particular sin, but fell victim to it anyway? The famous saying "the spirit is willing, but the flesh is weak" comes from this passage, and refers to the fact that it's easier to want to do the right thing than to actually do it.