Lutheranism is the sect that has caused the most damage in Europe throughout the ages, affecting everything from theological doctrine to philosophy to economy to commerce to popular culture, etc. This is, in part, because it synthesized and further transmogrified the errors of the heresiarchs of previous ages (i. e., Pelagianism, nominalism, etc.). It was, in a real sense, an prototype of modernism.
One of the greatest flaw of Lutheranism is how it has debased the notion of grace, one of the most important and impacting questions of theological discourse.
Rev. Father Garrigou-Lagrange in his work
Three Ways of the Spiritual Life [
Les trois conversions et les trois voies], (Westminster, MD: Newman Press, 1950), shows how the Lutheran heretics have degraded the notion of grace and what is the true nature of supernatural grace according to the teaching of the Church.
Take special note of the footnotes on pp. 5-6.