Hi Sam, sure. Here are a few reasons:

1) The original text of verse 37 contains a repetition of the words “yes” and “no”. Literally it says, ‘but let your word be “yes, yes; no, no”’. I would translate this something along the lines of, “Make sure that your yes means yes, and your no means no.”

2) In the immediate context, in this part of the sermon on the mount, Jesus is taking various commandments (e.g. about murder, adultery, etc.) and radically deepening their application so that they don’t just address the external circumstances but apply to the heart itself. It’s likely that he’s doing the same thing here - i.e. he’s not interested in external forms of promises (whether or how you swear oaths), he’s interested in faithfulness.

3) The reason Jesus gives for not swearing oaths is that God is involved with and has control over everything in the world and in our lives. The problem with the whole idea of an oath is that it assumes that some promises are binding (because they’re formally related to God by an oath, for example), while others aren’t (because they’re not connected with God). But our faithful Father is interested in all the promises of his Sons.

4) If you’re interested in the alternative Pharisaical interpretation of the 3rd commandment that I mentioned in the post, check out the Mishnah Shebuoth. This helps us to see what kind of thing Jesus was probably reacting against (loopholes, exemptions, etc.).