The Epistle to the Romans, written by the Apostle Paul, explains to us the true meaning of the teaching: "For the wages of sin is death, but the gift of God is eternal life" Romans 6:36.
The law of the return ("do not be deceived:God cannot be mocked. A man reaps what he sows", Galatians 6:7) is a universal rule, in men's life there are two poles, two possible  directions opposite to each other: the ruin or the eternal life. Because there are two lifestyles: a life full of sins or a life of retitude. The retitude is defined as the Golden Rule: "Do for others what you would like them to do for you" Matthew 7:12 The parable of the Good Samaritan (Luke 10: 25-37) explains this problem. We act as the Pharisee who passes by or the Samaritan.
The difference is the empathy, a faculty of the spirit, the neighbor matters or not. But this goes beyond, because the sin means "to fail". Sin is a lost of reason and the love for God and the neighbor. When we sin we are only interested in our ego, our money and vices, in short we are focused only in ourselves, or if you prefer we only love ourselves. Improve and do well, that 's no matter. The law of the return acts. The long-term return of the error or the sin is what explains the verse, death and ruin.
The world gives us back what we give. Sin is evil, and evil does not lead us to happiness but to our ruin. However the good deeds, the actions free from error, progressives, correct and just lead us to the perfect happiness: happiness of the heart and this is Eternal Life, and this is where the good and selfless love, the love for God and the neighbor appears. As we see the forms of love are transformated into lifestyles towards the society. Ethics teach us, that we have to choose between good and evil, between sin and righteousness.
It is a fundamental human choice, there is no middle ground in ethics we are saved or condemned.