What is the main conflict in The Protestant Ethic and the Spirit of Capitalism by Max Weber?

Weber notes that the Christian of the Middle Ages lived ethically but his good deeds did not represent a life-time of devotion. The Catholic held that the absolution of the Church made up for his imperfection and sin. It was the Catholic priest who held the key to salvation through his ordained position and relationship with God. The priest was able to forgive sin in the name of God. The Calvinist could not hope for such forgiveness and ease of consciousness and his thoughts had to be constantly focused on salvation. This was the fundamental conflict between Catholicism and the Reformed faith.