Matthew 5:36
Nor should you swear by your head, for you cannot make a single hair white or black.
What it says
Jesus says a person cannot make even one hair white or black.
What it is doing
The verse exposes human limits in self-guarantee.
In context
33Again, you have heard that it was said to the ancients, ‘Do not break your oath, but fulfill your vows to the Lord.’ 34But I tell you not to swear at all: either by heaven, for it is God’s throne; 35or by the earth, for it is His footstool; or by Jerusalem, for it is the city of the great King. 36Nor should you swear by your head, for you cannot make a single hair white or black. 37Simply let your ‘Yes’ be ‘Yes,’ and your ‘No,’ ‘No.’ Anything more comes from the evil one.