One of the earliest Christian writings which despite its ancient origins did not get included in the Christian Scripture is the writing known as The Didache. It was written probably in the late 1st Century, shortly after the other New Testament books were written. In it we see some of the focus of early Christians and their thinking on how to live the Christian life in world which was often hostile to the Christians. Here is a brief excerpt from The Didache:
There are two ways; the one is that of life and the other is that of death. There is a great difference between the two ways. The Way of Life is this: first, you shall love the God Who made you; second, you shall love your neighbor as yourself. Everything that you do not wish to be done to you, do not do to another!
Bless those who curse you, and pray for your enemies. Fast for those who persecute you, for what grace would you receive if you love only those who love you back? Even the heathen do that. Love those who hate you, and you will have no enemies. If someone strikes you on the right cheek, turn the other to him also, and you will be perfect.
You shall not be rapacious and always want to have more, or be deceitful, or malicious, or imagine yourself to be great. You shall not plot evil schemes against your neighbor. You shall not hate any man. You shall admonish people, you shall pray for people, and you shall love man more than your own life.
Do not grumble, for this leads to blasphemy; do not be self-willed or evil-minded, for all these things breed blasphemy. Be gentle-minded, for those of a gentle mind shall possess the earth. Be patient and have a loving heart. Be guileless, quiet and good, trembling in all things at the words you have heard. You shall not exalt yourself or allow your heart to be bold or presumptuous. Your heart shall not cling to the high and mighty on earth but to the good and humble folk. (George Grube, What the Church Fathers Say About…, pp. 137, 138, 139)