Previously Jesus told his hearers that God's throne, footstool, and earthly home are not theirs to swear by. Here he says that they may not swear even by their own heads.
Jesus is talking to a group of people about what might happen to them as individuals. All occurrences of these words are singular, but you may have to translate them as plurals. (See: [[rc://en/ta/man/translate/figs-you]])
# swear
This refers to taking an oath. See how you translated this in [Matthew 5:34](./33.md).