The arrival of Jesus signalled the beginning of a new era. God entered history in a personal way, and made it unmistakably clear that he is on our side, doing everything possible to save us. It was all presented and worked out in the life, death, and resurrection of Jesus.
It was, and is, hard to believe — seemingly too good to be true. But one by one, men and women did believe it, believed Jesus was God alive among them and for them. Soon they would realise that he also lived in them. To their great surprise they found themselves living in a world where God called all the shots — had the first word on everything; had the last word on everything. That meant that everything, quite literally everything, had to be re-centred, re-imagined, and re-thought. They went at it with immense gusto.
They told stories of Jesus and arranged his teachings in memorable form. They wrote letters. They sang songs. They prayed. One of them wrote an extraordinary poem based on holy visions. There was no apparent organisation to any of this; it was all more or less spontaneous and, to the eye of the casual observer, haphazard. Over the course of about fifty years, these writings added up to what would later be compiled by the followers of Jesus and designated The New Testament.
Peterson, Eugene H. The Message.
The NT authors were all men of God and were steeped in the Jewish Scriptures that form the Christian Old Testament. Even the Gentile Luke, the author of the Gospel in his name and the Acts of the Apostles, new of the traditions of the Jews. All the authors either alluded to or made direct reference to these Scriptures. A list of the direct references can be found by clicking here.
A key part of the New Testament is affirmation of the Holy Spirit as part of the Godhead, a divine person in his own right. Click here for the attributes of the Holy Spirit.