Matt 5:33--37 Jesus instructs on Making Vows or Oaths.

Mat 5:33  "Again, you have heard that it was said to the ancients, 'THOU SHALT NOT SWEAR FALSELY, BUT SHALT PERFORM THY VOWS TO THE LORD.'

Mat 5:34  But I tell you not to swear at all; neither by Heaven, for it is God's throne;

Mat 5:35  nor by the earth, for it is the footstool under His feet; nor by Jerusalem, for it is the City of the Great King.

Mat 5:36  And do not swear by your head, for you cannot make one hair white or black.

Mat 5:37  But let your language be, 'Yes, yes,' or 'No, no.' Anything in excess of this comes from the Evil one.

To swear falsely [To COMMIT PERJURY], n. [L. perjurium.] The act or crime of willfully making a false oath, when lawfully administered; or a crime committed when a lawful oath is administered in some judicial proceeding, to a person who swears willfully, absolutely and falsely in a matter material to the issue.

WIKIPEDIA Definition : Perjury, also known as forswearing, is the intentional act of swearing a false oath or of falsifying an affirmation to tell the truth, whether spoken or in writing, concerning matters material to an official proceeding.[1][A

Mat 5:33  "Again, you have heard that it was said to the ancients, 'THOU SHALT NOT SWEAR FALSELY, BUT SHALT PERFORM THY VOWS TO THE LORD.'

Perjury?

BUT thou SHALT PERFORM THY VOWS TO THE LORD.'

Perform unto the Lord thine oaths - The morality of the Jews on this point was truly execrable: they maintained, that a man might swear with his lips, and annul it in the same moment in his heart. Rab. Akiba is quoted as an example of this kind of swearing.

Perform unto the Lord - Perform literally, really, and religiously what is promised in an oath.

‘but do what you have vowed to the Lord to do.' GNB

http://media.nj.com/yankees_main/photo/roger-clemens-testify-perjury-charge-819jpgjpg-efe020a5aa8022b0_large.jpg

Mat 5:34  But I tell you not to swear at all; neither by Heaven, for it is God's throne;

Leon Morris :“Jesus command is Emphatic,  ‘Do Not swear at all’”.

To swear means: “To make a solemn declaration or statement with an appeal to God or a superhuman being, or to some sacred object, in confirmation of what is said.” Shorter Oxford Dictionary.

Swearing could be considered as self-cursing if one is not telling the truth.

For the followers of Jesus this was not necessary.

Mat 5:35  nor by the earth, for it is the footstool under His feet; nor by Jerusalem, for it is the City of the Great King.

Mat 5:36  And do not swear by your head, for you cannot make one hair white or black.

Mat 5:37  But let your language be, 'Yes, yes,' or 'No, no.' Anything in excess of this comes from the Evil one.

We should never be pushed to make an oath before telling the truth.

Just let your “Yes, be “Yes” and your “No” be “No”. James 5:12

Anything more than this is “of the Evil One”. It originates from the devil.