Thank you for the question on New Testament and New Covenant, “Is there a difference between the New Testament and the New Covenant? If so, when did the New Covenant become effective?”
For individuals who are not familiar with biblical or Christian words, terms like New Testament and New Covenant can be confusing.
Here are some thoughts on the New Testament and the New Covenant:
A. The words, New Testament, refer to the second part/division of the Bible.
The Bible is viewed as Old Testament and New Testaments. The words, Old Testament, refers to the books that begins with Genesis and ends with Malachi. There are 39 of them. This is followed by 400 years of silence. The New Testament begins with the Gospel of Matthew and concludes with Revelations. There are 27 letters/writings in the New Testament.
B. The words, New Covenant, is associated with the last Passover of Jesus.
Jesus and his disciples were celebrating Passover which is a commemoration of the angel of death by passing the homes that had blood place on the doorway. This was the 10th Plague that also signal their deliverance from Egypt. On that day, the Jewish families were to kill a lamb, place its blood on the door way and eat it with bitter herbs.
Jesus took that imagery and declared that his death would pave the way for the forgiveness of sins whereby death would pass over them. The bread represented his body in which he took the sins of the whole world upon his own body and the cup represented his shed blood for the forgiveness of sins.
Jesus used the word, covenant in Matthew 26:26–29, Mark 14:14–22–25 while Luke records the words, new covenant, in Lk. 22:19–20 and I Cor. 11:23–26. The concept of Testament or Covenant has to do with an agreement, a promise between two parties. It may be conditional or unconditional.
Jesus was inaugurating a new promise of forgiveness of sins through his body and shed blood that no longer required animal sacrifices for the covering of sins. This last Passover is now refer to by Christians as the Last Supper of Jesus or Holy Communion.
On a side note there is a reference in Jeremiah 31 of a new covenant with Israel that the commands of God will be in the believer’s hearts rather than upon the believer’s heart. Thus the term, new covenant, can refer to a future change of hearts for the nation of Israel or the promise of forgiveness of sins through Jesus Christ that is apart from the Mosaic Law.
SUMMARY: The New Testament refers to 27 books of Jesus and the writings of the Apostles while the New Covenant refers to promise by Jesus of the forgiveness of sins and deliverance from death through him through two elements: bread and the cup.