The Bible teaches us that with lies came oaths; because in essence the oaths are used to give credibility to the claims of the man. A lie can be free for the one who tells it, but it can be expensive for the one who receives it, lying in many cases can become a very harmful sin. The oaths in the Sacred Scriptures were particularly important, because the law of Moses was made for the carnal man, the man subject to the slavery of sin: "Again, you have heard that it was said to the people long ago, ´Do not break your oath, but fulfill to the Lord the vows you have made.´" Matthew 5:33.
But Jesus tells us that to enter the Kingdom of Heaven we must always proceed with the truth: "But whoever lives by the truth comes into the light, so that it may be seen plainly that what they have done has been done in the sight of God" John 3:21.
The truth for Jesus is the starting point of everything, because the truth brings assertiveness in the face of problems, the truth is precision and accuracy. People who live according to the law of the spirit do not need to swear by anyone or anything, because what they do and what they say is subject to the logic of the spirit, when a person lives according to the will of God there is no "this is yours" or "this is mine", but simply "everything belongs to everyone". God's grace frees us from selfishness and deceit.
Jesus then explains to us that we must be simple and direct people, without hiding anything and not swearing by anything or anyone, and so we proceed like the Father who is wise and perfect: "But I tell you, do not swear an oath at all: either by heaven, for it is God's throne; or by the earth, for it is his footstool; or by Jerusalem, for it is the city of the Great King. And do not swear by your head, for you cannot make even one hair white or black. All you need to say is simply ´Yes´ or ´No´; anything beyond this comes from the evil one" Matthew 5:34-37.