"Do not swear at all: either by heaven, for it is God’s throne ..." (Matthew 5:33-37)

“Again, you have heard that it was said to the people long ago, ‘Do not break your oath, but keep the oaths you have made to the Lord.’ But I tell you, Do not swear 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. Simply let your ‘Yes’ be “Yes,’ and your ‘No,’ ‘No’; anything beyond this comes from the evil one." (Matthew 5:33-37)

Is Jesus talking about cursing?

Note that the word "swear" is not referring to swear words, or what is commonly referred to as cursing.

The word "swear" is being translated from the Greek word ὀμνύω (omnyō). This means "to affirm, promise, threaten, with an oath" - relates specifically to making a promise upon something else.

For example, when we say "I swear on (fill in the blank) that this will happen," we are giving an oath, and swearing or promising on that particular (blank).

In other words, a more appropriate translation of the Greek word ὀμνύω (omnyō) would be giving an oath, or making a promise.

What does Jesus mean by 'people long ago'?

Jesus is speaking of the teachings of the prophets, who taught people in centuries past. This illustrates again the importance of time and circumstance within the teachings of the prophets including Moses.

Jesus is speaking of something specific taught by the prophets before him. While the exact statement is not in the current Old Testament, Jesus is likely paraphrasing this instruction by Moses:
When a man makes a vow to the LORD or takes an oath to obligate himself by a pledge, he must not break his word but must do everything he said. (Numbers 30:2)

No oaths at all?

Now Jesus is instructing his students not to make oaths at all - especially not oaths taken using the Supreme Being or those elements considered sacred - including the city of Jerusalem.

"The Great King" that Jesus is referring to is the Supreme Being.

This is not fully a contradiction to Moses' instructions, as we find that Moses did discourage making oaths without careful consideration:
"...if anyone thoughtlessly takes an oath to do anything, whether good or evil (in any matter one might carelessly swear about) even though they are unaware of it, but then they learn of it and realize their guilt..." (Lev. 5:4)
Only God has the ability to truly control events. When a person “swears by heaven” or “swears by the earth,” or “swears on his mother’s grave,” or “swears by God,” these are oaths or promises wherein the giver is attempting to promise something that cannot be guaranteed using something that is spiritually sacred.

Jesus is clarifying that one should not utilize those things that are sacred - because of their relationship with the Supreme Being - for the purpose of one's self-centeredness.

Furthermore, any oath or promise made is shortsighted because we are not in control. Therefore, Jesus is suggesting to his students that they do not utilize the Supreme Being's Holy Names or references out of context - and stick with honesty and sincerity about the things they know, and speak without duplicity.

This is also captured by the instruction of Moses:
“You shall not take the Name of the LORD your God in vain" (Exodus 20:7)
The Holy Name of the Supreme Being has been cherished by God's loving servants since the beginning of time. Calling out, singing, or otherwise, the incantation of His Holy Names is an observance that can purify our consciousness and bring us closer to the Supreme Being. This is evidenced throughout the scriptures.

Here Jesus is discouraging making oaths or promises in general. This relates to the fact that we are not in control. We cannot even control whether our hair turns gray or not - let alone whether we can live up to a promise in the future. This statement affirms that the Supreme Being is in control and we are not.

Jesus is encouraging his students to keep it simple, and avoid duplicity and making promises that cannot be kept.

Who is the 'evil one'?

Who might this "evil one" be, who would be making promises that might not be able to be kept? Would this be another person besides ourselves? If we start making undoable promises can we blame someone else for it?

We cannot blame someone else. In fact, there is no word in the original Greek that can be translated to "one.” There is only the word πονηρός (ponēros), which means "full of labours, annoyances, hardships," and "bad, of a bad nature or condition: in a physical sense: diseased or blind," according to the lexicon.

Jesus is describing our diseased condition combined with the illusory nature of the physical world - the false pretense that we are these physical bodies and the forms and things around us belong to us.

This illusory energy reflects our self-centeredness. It reflects our desire to play the big man. We want to be supreme. We want to talk big - we want to seem in control. The illusory nature of the physical world - as we misidentify with these temporary physical bodies.

In other words, evil is the state of rebellion against God. Evil is the state of consciousness that says: "I don’t care about God, I’m going to go ahead and do what I want. I am powerful."

Is this what Adam did??

This is the very rebellion that is at the core of Adam disobeying God in the Garden of Eden. While we might want to blame Eve, or blame the serpent, or even blame the tree of knowledge itself, the actual act that effectively banished Adam (symbolizing each of us) from the Garden was the disobeying of God’s instruction.

This rebellion of the Supreme Being lies at the root of the reason each of us is here in this physical dimension, away from Him. We have been "cast out" of the spiritual realm and given these temporary physical bodies to try to play out our self-centered desires within this temporary physical dimension.

And it is our continued rebellion of His instructions and His messengers that keep us away from Him. This is the state of evil. Evil is a state of rebellion from our natural position of being one of the Supreme Being's loving servants and friends.