Only when he was listening to Ponticianus describe the monastic joys of serving God in chastity did Augustine see the damage that his carnal indulgences had done to his soul. He saw in his mind's eye that he was "crooked, filthy, spotted, and ulcerous" (173). Not that the bodily urges did not serve a good purpose as well as an evil one in Augustine's philosophy. Central to his faith was the idea that all things come of God, and that all things that come of God must be good. This includes the senses and their desires. He conceded that sexual activity does indeed have its place in the creation of children, but only within the confines of marriage -- and even then, the gratification of sexual desire serves as an impediment to faith. As for the other physical senses, they too have their place in the sustenance and maintenance of the body, but they are easily liable to corruption.

It is the lust after...

When discussing the sin associated with eating and drinking, he clarifies: "It is not any uncleanness in the meat that I fear; it is the uncleanness of gluttony" (240).
The most dangerous concupiscence of all for Augustine is not the satisfaction of carnal desires like food or sex, but the quest for knowledge through the bodily senses instead of through faith. The dangers of "acquiring experience through the flesh" (245) in the form of learning and science are the most insidious for Augustine, and were the ones that he himself struggled the most to overcome.

References

Origen. The Writings of Origen. Alexander Roberts and James Donaldson, eds. Edinburgh: Elibron, 2004.

Augustine. The Confessions of St. Augustine, trans. Rex Warner. New York: New American Library, 1963.