Unlike Aquinas, Augstine was very autocratic and dogmatic. Augstine believed that how human-beings, at the current (contemporary) time, are not how they ought to be. Therefore, they need a strict principle like the "idea" (This indicates Augstine was strongly influenced by Plato) to guide them to how they should be. The problem of his idea is that there is "no stop point" where all human-beings are fulfilled in what God, the idea, claim. That's why Augstine stated. Aquinas was more realistic and Augustine. Aquinas at least knew how human-beings are at the current (contemporary) is what God initially planned them to be. So, we can neither complain nor expect them to be at the ideal state. Aqunas argued that we coexist with our sins but we have to resist against it as much as possible. However, from my point of view, sin is a reality, and sin can be necessary. I do not see sin to be always something to be avoided; it is often a necessary to enjoy our life !!
Well, you have to imagine what the community was like in the early medieval age. Collapse of Roman Empire, havoc everywhere, and so people lost their direction in their life. Unlike nowadays when we can access to various information resource and be educated with Copernican world view, people at the medieval age were disparate to believe in something superstitious.... oh it should be said the superstitious worship was "necessary" to give people a certain principle as the "natural law", the universal invincible law. But, this explanation does not mean I support it: Actually I think of this divine rule was necessary evil at the contemporary time period. As a matter of fact, I reckon the late medieval age (about from the 3rd Crusader period) when people gradually became independent from this Christian autocracy. This was the sign that that part of the world became more stabilised, the technology advanced, and the information flow grew.
Furthermore, I highly admire all 3 Palestinian religions, Judaism, Christianity, and Islam. These religions enlightened people to think independent from the nature surrounding them. Neither all ancient religion nor all oriental religions have ever done in such a way! The Palestinian religions enabled individual human-beings to think rationally (beyond their surrounding nature and their box of thought), and established strongholds! Augstine and Aquinas definitely contributed in this great work!