Summa Contra Gentiles — Book 4, by Aquinas is the masterpiece of an inexorable exceptional writer wholly concerned with the truth that surpasses reason."Salvation" revolves around the four mysteries of Christian belief: the Trinity, Incarnation, Sacraments, and Resurrection. For each of these, Aquinas demonstrates their truth based on scripture and philosophy. Aquinas, blessed with the most extraordinary mind of his time, pursues the mind of God with his usual unsurpassed intuition and clarity. Time and intellectual energy invested in reading this are richly rewarded!