The genius of the “Summa Theologica” was that it was a successful synthesis of both pagan and Christian knowledge, and it made Christianity seem reasonable. The public generally accepted it, and it worked for hundreds of years.
The root of the intellectual problem with Christianity today is that knowledge has exploded, and much of what has become known over the last few hundred years is inconsistent with traditional Christian ways of thinking. The general public views the Christian attempts to synthesize the new information as being inadequate, and has consequently turned its back on the church. Christians, for their part, have frequently responded by simply rejecting scientific information that conflicts with their beliefs, which is hardly a selling point for religion in the 21st century.
What Christianity needs, in effect, is a new “Summa Theologica.” Since Aquinas had far less material to deal with in his day that Christians do today, this would be a much more difficult task, and might be impossible. Only an amazingly brilliant and audacious man would even attempt it. Without it, however, Christianity is heading for an intellectual cave.