Again, you have heard that it was said to the people long ago, ‘Do not break your oath, but fulfill to the Lord the vows you have made.’  But I tell you, do not swear an oath at all: either by heaven, for it is God’s throne;  or by the earth, for it is his footstool; or by Jerusalem, for it is the city of the Great King.  And do not swear by your head, for you cannot make even one hair white or black.  All you need to say is simply ‘Yes’ or ‘No’; anything beyond this comes from the evil one.

This section is not saying don’t take marital vows or do not enter into business contracts. The problem was that the Pharisees had many a loophole that they felt justified them when they took an oath and could break it. They even had it in writing which oaths were binding and which oaths were not (in the Mishnaic tractate Shebuoth). They were not looking for a way to keep their oaths but a way to get out of their oaths.

With those oaths, which one was binding depending on what was sworn upon. Things such as the earth or God’s throne or his footstool or by Jerusalem. But God says it doesn’t matter what you take your oath upon. These are all of God. Rather be someone who keeps the commitments that you’ve made. Anything else comes from the evil one.

Why would it be considered from the evil one? If you take an oath with the hope/intention of finding an escape clause, you are being deceitful. That is evil. If you do not fulfill your commitment, then you are also of poor character and that is not of God.

Jesus is saying mean what you say and do it. If you do that, you don’t even need to take an oath. Be a person of your word. No loopholes, no weasling out of things, no frivolous lawsuits to try to get ungodly gain.

Just do what you say you will do. That’s it. Simple.