In 1543 the Council of Trent met and Wednesday marked the 450th anniversary of its closure. It is worth noting that the background to the Council is quite similar to the condition of the Church today, there where sexual scandals exemplified by the Borgia, there was partisan careerism exemplified by the Rovera pope, the fearsome warrior Julius II, there were financial scandals, the selling of indulgences by the same pope, there was even a 'gay lobby' on the part of many Curial officials - remember half a century before 'the Greek vice' had been a particular target of Savonarola,
To regard the period before Trent as being a time of doctrinal clarity is to demonstrate both an ignorance of history and to underestimate the importance of the great Council. In England Lollardy had existed since the mid-fourteenth century as an undercurrent, the same in Northern Italy and Switzerland with Waldensians, the great European heresiarchs of the 16th century built on an already established foundation.
Popes, bishops, priests, abbots, monks along with Emperors, kings and other magnates exploited the faith for their own personal and political advantage. Spurious doctrines tinged with superstition were as common as spurious relics. When heresy reared its head as a new intellectual fashion, the clergy, for the most part, either took it up or because of ignorance were ill equipped to combat it. In Northern Europe principality after principality fell away from the true faith leaving the definitions the Catholic belief ragged and the clergy and faithful demoralised.
If one wishes to understand what was wrong before, or where the Church and it teaching was weak and under attack, it is well worth looking at what Trent saw as important. Its major concern seems to have been the reform of the clergy, not just their intellectual development but their spiritual and moral formation, concubinage, simony, empty benefices, lack of pastoral care, the lack of an evangelical example, seem to have been as much a problem as shaky theology. The new technology of movable type meant that for the first time not only could the Church's theology be made widely available but also its Rites could be standardised with greater ease than with costly manuscripts - it is worth noting that pre-Trent Pontificals were more or less rites peculiar to each diocese. Trent spent a great of time on Justification and Grace because the Medieval theology was imprecise, ultimately giving an imprecise image of God, before moving on to re-write the Rites. The development of the 'Tridentine Mass' is interesting, other Rites were permitted providing they had a 200 year pedigree, which presumably would suggest providing that they were free from nascent Protestantism or exaggerated local preference.
What Trent does with great force is to introduce Thomism into the centre of Catholicism as a unifying force rather than as a possible option, a school of theology amongst other schools. At the most obvious level Trent makes Thomas' definition of Transubstantiation de fidei because previous teaching on the Real Presence was imprecise and open to misreading.
I see liberalism and confusion as being the 'spirit' of Vatican II, Ultramontanism as the 'spirit' of Vatican I. The 'spirit' of Trent is perhaps seeing too harsh a break between the theologies that united East and West before the Great Schism. Trent in many ways marks a Westernisation of Catholicism, as the decline and fall of Constantinople a century before mark the Orientalisation of Orthodoxy. For Catholicism the fruit of the Reformation, because of the Fathers of Trent, was the Glorious Counter-Reformation.
Stephen Beale has a very worthwhile article: Lessons from the Council of Trent:
The achievements of the Counter-Reformation are breathtaking: It gave rise to great religious orders like the Discalced Carmelites, the Capuchins, and the Jesuits, who, in turn launched the great missions to South America, Africa, China and Japan. It gave birth to great saints like St. Teresa of Avila, St. John of the Cross, St. Ignatius of Loyola, St. Philip Neri, and St. Francis de Sales and inspired a new era of devotional fervor, as exemplified in books written by many of those saints, like The Spiritual Exercises and An Introduction to the Devout Life. And it created the form of Catholicism that withstood centuries of social strife and political turmoil, from the French Revolution to the emergence of communism...