In order for us to elaborate on your statement, let us first think about what ethics are, and then about what Christian ethics are. Ethics can be defined as a set of rules upon which we base our behaviors. We derive these rules from our concepts about which things are morally right and which things are morally wrong. In other words, in order to have ethics, we also have to have moral values. In Christian ethics, the moral values come from Christian doctrine and teachings. Thus, we can say that Christian ethics are a set of rules that we live by which are based on Christian beliefs and values. With this in mind, let us consider your statement and elaborate on it.
According to your question, “it is the faith of Christians that defines their character and motivates their course of action.” The first thing we need to think about is how faith motivates Christians’ courses of action. We can say that a Christian’s faith gives that person a set of beliefs and values. These beliefs and values inform the ethical rules that that person follows. A non-Christian might have a very different set of values and, therefore, might have different ethical rules.
For example, let us think about alcohol use. A non-Christian might think that it is fine to get drunk as long as they do not do anything that will hurt anyone else. But a Christian person’s faith might motivate them differently. For example, a Christian might believe in the basic idea that he or she should always act so as to avoid sin. Even if drinking in itself is not a sin (an issue that is controversial among Christians), a Christian might want to avoid drinking because it can lead to sin. A person who gets drunk is likely to lose his or her inhibitions and might well engage in things like improper sexual activity. Therefore, a Christian might hold that getting drunk is unethical and wrong where a non-Christian would not. In this way, the Christian’s faith motivates his or her course of action.
The second aspect of your statement is the idea that faith defines a Christian’s character. We can say that the strength of a Christian’s faith determines how strongly they will stick to their ethical rules. A Christian with a stronger faith, we can argue, is less likely to break his or her ethical rules. In other words, all Christians might share similar ethical rules, but those whose faith is stronger might be less likely to violate those rules.
Thus, we can see that Christian faith affects the ethical rules that people set for themselves. We can also see that the strength of a Christian’s faith determines how strongly he or she will stick to their ethical rules.