As Augustine wrestled with Christianity and whether or not to embrace it, he struggled with sexual immorality. Possessing a long time concubine, through whom he fathered a son, Augustine refused to end this affair. Even after his amazing conversion, which, at least in Augustine's mind, only occurred after targeting this vice, Augustine still struggled in this area. Perhaps this "thorn in the flesh" contributed to Augustine's eventual realization concerning the burden of sin and the need for grace: if not for the work of God through His Spirit in the heart of man, he would go on sinning out of a love for wickedness. Augustine knew all too well that cooperation in grace for salvation defied not only Scripture, but it also flew in the face of reality.

Study Guide Part 1:
https://store.ligonier.org/a-survey-of-church-history-part-1-study-guide?utm_campaign=agtvstudyguides&utm_source=agtv