Matthew 5:35
or by the earth, for it is His footstool; or by Jerusalem, for it is the city of the great King.
What it says
Jesus forbids swearing by earth or Jerusalem because they also belong to God.
What it is doing
The verse extends the rejection to more sacred references.
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.