No longer a virtue or work, faith became confidence in God's Gospel promise. The Church of the Middle Ages had taught that faith saves only if it is made complete by good works. Luther reasserted the Biblical teaching of faith, that faith saves apart from good works. Faith is that which receives the offered gift of forgiveness through Jesus Christ. It is the empty hand that takes the gift.
Faith alone saves.
Faith plus nothing saves. From uncertainty and insecurity to certainty and security in Christ. The Christian was no longer intentionally strung out between hope and fear, but through faith in the Gospel now lived in hope and joy. The Christian was now certain that he would enter heaven when he died. Prior to the Reformation, people put their energy into doing works in order to save themselves.