Matthew 5: 33-37
What is an Oath?
1 a solemn promise, often invoking a divine witness, regarding one's future action or behavior: they took an oath of allegiance to the king.
2 a sworn declaration that one will tell the truth, especially in a court of law: each took the oath and then gave evidence.
Why was it deemed necessary?
Oaths in the Bible
The Heart of the matter - Jesus Says Let Your Yes be yes & No be N