Jesus advises us not to swear at all, but to say simply, "Yes" or "No" (verse 37). If we are honest, we have no need to take an oath. He goes so far as to say that anything more than "Yes" or "No" has its source in the father of lies (John 8:44)!
There are several aspects to these verses. The overall statement Jesus makes is that we do not need to swear by anything to confirm that our statements are true. A Christian's word should be his bond, as the old saying goes. We should be so bound by the ninth commandment that nothing else is necessary.
The not-so-obvious meaning of these verses is that we should not lightly give an oath or make a vow to God to acquire something. We have many desires, and some might take it upon themselves to ask God for them, promising to perform a certain deed if He gives it to them. Jesus warns that once we get what we want, we may forget what we promised to perform. Numbers 30 shows that God does not take reneging on our promises lightly.
Should Christians make vows today? God tells us the best course to take in Matthew 5:34, "But I say to you, do not swear at all." James writes that it is best not to make them so we do not "fall into judgment" (James 5:12).
Though God advises us not to vow, we can still make vows if we so choose. In making one, however, we should consider the examples of Hanna and Jephthah. We should seriously contemplate what we are requesting and what we are promising, always asking ourselves, "Can I make good on what I've promised?"
We are a special people to God. He has called us, and has great love for us. He hears our prayers as we obey and love Him. We should give a great deal of thought to whether we need to make a vow when we have such instant and open access to the very throne of God. He does indeed hear our prayers, and He answers them according to what He sees is good for us. Why should we make vows when we know that He will give us or deny us what is best for us?
John O. Reid (1930-2016)
Should We Make Vows Today?