In the ancient Greek manuscripts of the New Testament, the word for “covenant”is diatheke, which also appears in the Septuagint version of the Old Testament as the translation of the Hebrew word b’rith. Diatheke can mean either a contract or a testament (as in “last will and testament”), depending upon the context in which it is used. In the New Testament there are instances of both meanings.
Jesus Christ of Nazareth, the central figure in the New Testament, is presented as the fulfillment of the new covenant prophesied by Jeremiah (Jeremiah 31:31-34). Jesus is the mediator or administrator of the covenant as a contract between God and the world. Jesus is also the testator, executor, and heir under his own testament (Hebrews 1:2; 9:15-18; 10:14-22). Anyone can become a joint heir with him by believing and following him. Jesus told the disciples that his was the blood of the new covenant serving as the sign and seal of it in the same way that Moses sealed the old covenant with the blood of a bull (Luke 22:20; Exodus 24:8; Hebrews 9:20).
Thus we see that the group of books called The New Testament got its name from the new covenant (or testament) promised in the Old Testament book of Jeremiah.
The four Gospels Matthew, Mark, Luke, and John relate Jesus’ birth, ministry, and death on the cross and also his resurrection, post-resurrection appearances, and ascension.
The book of Acts begins with the ascension, and carries through with the coming of the Holy Spirit, the beginnings of the first-century church, with emphasis on the adventures and ministries of Peter and Paul.
The 21 epistles are letters to specific congregations, or to Christians generally, explaining Christ and his teachings, and relating these principles to the everyday problems of the people.
The book of Revelation depicts a vision experienced by the apostle John in which he is given a message by God to be relayed to the churches. In his vision he sees heaven, the throne of God, and Jesus as the triumphant leader of angelic forces against Satan and the forces of evil.
With the exception of John’s writings, the books of the New Testament were written during part of the historical period covered by the book of Acts.