"Love must be sincere. Hate what is evil; cling to what is good" (Rom. 12:9, NIV).
"Do not be overcome with evil, but overcome evil with good" (Romans 12:21, ESV).
We are all born with an innate conscience capable of discerning right from wrong and applying abstract laws and rules to specific and concrete situations. Romans 2:15 says our conscience either excuses or accuses us: We all know God's law (natural law) but we flaunt it! Knowing better we still do wrong: "I know the better things and I approve them, and I follow the worst" (Ovid, Roman poet). Paul said, "...Who will deliver me from the body of this death?"(Rom. 7:24). "For I do not do the good I want, but the evil I do not want is what I keep on doing" (Rom. 7:10, ESV). None of us satisfies or fulfills our own expectations and standards--we all stand self-condemned. There are as many systems of ethics as there are worldviews, but basically, the Christian one assumes man is not basically good, but inherently evil and needs revelation and salvation from God to be convicted of right and wrong.
There is no such thing as perfectionism, or reaching a state of sinless perfection (cf. Prov. 20:9; Ps. 119:96). We all do things that we should've known better not to do! The law of Moses was given to convict us and show we cannot meet God's standards of righteousness, not to be a code of conduct to live by and earn salvation by merit. The requisite for salvation is to realize you cannot save yourself by good behavior and you need a Savior because of your sin, that you have fallen short of God's glory and standard.
Ethics with a capital E is nebulous for those who deny God--they dodge the no-absolute-truth thesis: "The absurd is, sin without God," said Albert Camus. Dostoevsky said that without God all things are permissible! Immanuel Kant said that God is necessary for ethics to be possible. The Nazis justified themselves socially and didn't think we had the right to try them for war crimes, but the allies appealed to "natural law." In academia, they teach you that ethics is about the good press (spin) and not getting caught! Social studies and psychology teach you to have good reasons for what you do and to have responsible decision making, as you make your own choices in life.
In antiquity, might made right and there was no universal ethic, and that is why Pilate asked, "What is truth?" Jesus claimed to be the epitome or embodiment of truth and also the way and the life to live. Postmodernists dodge the ethics issue, by saying there is no absolute truth and it is a nebulous thing to have one standard for everyone, as it evolves with society and situation (ethics). In other words, ethics are only relative! Today most students judge the usefulness of an idea, by its consequences or results, not its truth value--is it practical? Christians are urged to "overcome evil with good," and as the summation of ethics: "Follow Me [Christ]!" We are held to a higher standard and are the witness of Christ in the world as lights in the darkness and salt to preserve it and add flavor.
Christianity is not a list of dos and don'ts, nor a system of ethics; it's a living relationship of knowing a personal God. Ethics is the application of right doctrine and living it out by faith as our duty to God and man (cf. Gal. 5:6, NIV, which says: "The only thing that counts is faith expressing itself through love."). The faith you have is the faith you show! The law is written in all men: "The work of the law written in their heart, their conscience" (cf. Romans 2:15). People try to make up their own voluntary initiatives or codes of conduct to live by, but they are always ones they think they have kept or can. Christian ethics is based upon the exemplary, unequaled personality of Christ as the one to emulate, and He has no flaws--what a standard!
We all need a moral compass, and Humanists insist that they can have ethics without God, but Humanism is precisely that: Being as good as possible without God--which is a definition of evil. New age people will tell you to listen to the inner voice and to be in touch with yourself, and tolerance is the key, so don't be judgmental; if it feels like the truth to you, it is! the codes of conduct range from the Golden Rule (cf. Matt. 7:12), to the Brazen Rule of reciprocity or tit for tat, to the Silver Rule of not treating others the way you don't want to be treated--a negative Golden Rule, to the Iron Rule of treating others as a bully, where might makes right, and the survival of the fittest or social Darwinism is the rule. Most nonbelievers design their own ethics and don't adhere to an absolute standard of morality. Something they can comply with to their standards.
In the final analysis, the only true morality or ethics is when the motive, as well as the end result or goal, is pure and good: the means to the ends must be right, because the means do not justify the ends; and utilitarianism, or the greatest good for the greatest number, is another evil that has justified the murder of millions in communist countries. The premise that secular worldviews have is that man is basically good and can redeem himself, or lift himself up by his own bootstraps. Soli Deo Gloria!