“Again you have heard that it was said to the men of old, ‘You shall not swear falsely, but shall perform to the Lord what you have sworn.’ But I say to you, Do not swear at all, either by heaven, for it is the throne of God, 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 one hair white or black. Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil." (vv. 33-37)
Here, Jesus is condemning a practice that had become rampant and problematic: people would not swear by God's name and take it lightly, but they would swear by something else (the heavens, the earth, Jerusalem, their own head, and various others) and then consider it appropriate to take such an oath with breeze. His condemnation has one main point other than the obvious one of not swearing oaths lightly: swearing an oath by something seems to indicate that one has control over and own, and this is false. If one did not have some control or ownership over it, what difference does it make to swear by it or by nothing at all? I would say the answer is no difference. So swearing by something to make it sound more powerful is a mirage of honesty. Swearing by things instead of God such as his created bodies also does not bypass the problem that taking the things of God in vain is wrong.