Protestants have a generally common understanding of moral behavior: they largely agree that good works cannot save a person—only God can—but those who are saved will amend their lives to reflect their faith. Protestantism teaches that the individual is made right with God through faith in what God has done, not through any kind of virtuous behavior. That said, there is a wide variety of beliefs within Protestantism about how good works cooperate with God's saving grace, or follow upon salvation.
Lutherans and Reformed Protestants believe that good works play absolutely no role in salvation. Salvation consists in the forgiveness of sins, which is a completely free and un-prompted gift from God. Zwingli and Calvin agreed with Luther that even those elected by God to receive God's grace cannot perform works that merit salvation. The elect remain sinners, even after they have been justified through faith. This does not mean that any of the reformers taught that good works were not important at all. They were important to the reformers, and they are to most Protestants today. The only question was what role good works played in the life of a believer.
John Wesley and the Methodists following him (and much of American Protestantism in the wake of Wesley's influence) taught that good works—though performed only with the help of God's grace—definitely will accompany salvation, and that those who are saved can, through their own efforts, contribute to the process of Christian holiness, understood as thoughts, words, and deeds being motivated solely and purely by the love of God. Leading a life that is not marked by good works and that is marked by evil or immoral behavior can lead to the loss of one's salvation; thus the believer's behavior has a pivotal role in the ongoing experience of salvation, and thus the warnings against "backsliding."
All Protestant churches, therefore, have high expectations for moral behavior. Luther did not think works could save, but he did think that a good tree bears good fruit. The saved, freed from anxiety about their own salvation, can devote their attention to helping their fellow humans. They do so because the same work of the Holy Spirit that brought them to believe that their sins had been forgiven continues to work in them to do God's will. They do so because service to fellow humans glorifies God. And they do so because as they grow in the life of faith they become more Christ-like and so take on aspects of Jesus, such as seeing the image of God in everyone, even enemies, and reaching out to the poor and imprisoned, etc. While moral works are not necessary to retain salvation, such works will in fact characterize those who are saved. (The German sociologist Max Weber argued that Calvinists tend to be driven to perform works, not because they think works will save them, but because the ability to perform good works can be seen as a possible indication of God's grace, and a sign that one is among the elect.)
Calvin was also clear that even those who are not saved can and should also have high moral standards. Calvin makes this case as he argues (against those who think that the doctrine of predestination makes God into an unloving tyrant) that God cares for and showers grace on all humans, the saved and the unsaved. On the list of things that God gives even the non-elect are reason and will: reason to discern the good, and will to follow the good. In other words, the fact that there are well-ordered human societies in which it is possible to live and prosper is the direct result of God's endowing humans, whether saved or not, with a moral sense and the will to obey it. (But again, according to Calvin, moral behavior will not get a person into heaven.) Moral standards are clear, Calvin thinks, simply through the observation of nature (which, like the Bible, Calvin compares to a book written by God in which God's nature and will can be discerned). And since sin has blurred the vision of nature, God has in addition given the scripture (which acts in Calvin's metaphor like a pair of spectacles to sharpen vision), to clearly outline what God expects.
Debates in the Protestant tradition about moral principles have often originated in different interpretations of the Bible or in different applications made of the teachings of the Bible. For a long period in American history there was a fair amount of agreement on moral principles found in the Bible, largely derived from the Ten Commandments (Ex. 20:1-17) and Jesus' teaching (especially the Sermon on the Mount, Mt. 5:1–7:27). These include both moral virtues—such as honesty, marital fidelity, generosity, loving your enemies, business integrity, patience, care for the poor, humility, forgiveness—and Christian practices, such as regular prayer, almsgiving, fasting, community worship, etc. (The obvious exception to this common platform of values was whether the Bible allowed or forbade slavery.) Protestants joined together in the temperance movement, prison reform, labor laws, etc.