St Thomas Aquinas, Bishop and Doctor, is most noted for his theological writing. If you find your understanding of doctrine and faith is challenged by confusion and want a simple, straightforward and uncompromising guidance - then choose to read St Thomas.
His masterpiece is perhaps the Suma Theologica. The Suma was for a very long time the standard textbook or reference for theological certainty and is still so valuable today. Beware of an urge to study it - it will take you a lifetime or two to get to grips with it.
Somewhat like St Benedict's Rule on monastic life, the Summa begins with an exemplar of clarity:
Because the doctor of Catholic truth ought not only to teach the proficient, but also to instruct beginners (according to the Apostle: As unto little ones in Christ, I gave you milk to drink, not meat—1 Corinthians 3:1-2), we purpose in this book to treat of whatever belongs to the Christian religion, in such a way as may tend to the instruction of beginners. We have considered that students in this doctrine have not seldom been hampered by what they have found written by other authors, partly on account of the multiplication of useless questions, articles, and arguments, partly also because those things that are needful for them to know are not taught according to the order of the subject matter, but according as the plan of the book might require, or the occasion of the argument offer, partly, too, because frequent repetition brought weariness and confusion to the minds of readers.
Endeavouring to avoid these and other like faults, we shall try, by God's help, to set forth whatever is included in this sacred doctrine as briefly and clearly as the matter itself may allow.