The next in Jesus’s series of 6 interactions with the OT law has to do with oaths. In this section Jesus pulls two phrases from the OT which interpreters of his day may have been combining (Lev. 19:12; Num. 30:2). The phrases warn against swearing by God’s name but not fulfilling what you vow.
In order to protect themselves against breaking this law and incurring judgment, the people took to swearing their oaths by other things: the earth, Jerusalem, the temple, the gold of the temple (Mt. 23:16), and even their own heads. They could make an oath that sounded important but if they failed to complete it they were in no danger. Or so they thought.
In his response, Jesus makes two moves. First, he shows that failing their new vows is just as damning because they infringe upon God just as swearing by his name does. The earth is God’s throne. Jerusalem belongs to the King. So just by changing the words they have not succeeded in escaping through a lexical loophole.
But just as we have seen him do in the previous passages, he goes a step further. He says not to swear at all (34). Why not?
Oaths exist because honesty does not. Oaths are either an attempt to secure honesty from others through threat of judgment (e.g. court witnesses swearing on a Bible), or to convince others of our sincerity (“I didn’t wreck the car! I swear to God!”). We swear because we lie. What Jesus envisions is a world where people can be taken at their word. A world where we speak unequivocally. Where yes means yes and no, no. A world where we don’t have to add words to undergird the accuracy of our other words.
The kingdom of God is founded on the Truth-speaking and Word-keeping of God. Jesus is saying that people of the Word should be people of their word.