In Jesus’ time, there were no written contracts, because the price of ink and paper was prohibitively expensive. In fact, it’s estimated that the cost to pen each of Paul’s epistles was in the thousands of dollars, some say anywhere from $2,000 to $40,000 a piece! The excessive cost of writing things down demanded that there be another protocol for making legal agreements in the ancient East. In Jewish culture, the custom was that a consensus was reached, the parties would shake hands, and then they would swear by the Name of God that they would keep their promise. In essence, when they invoked the Lord in any agreement, they made a verbal contract. This was an important part of the legal system of the day.
Though I don’t know this for certain, I’m guessing that the ease of making such contracts caused the process to become a bit too common. Understanding human nature, I’m pretty sure that people began cutting corners, and in an effort to create optionality, or the ability to get out of a legal agreement, they started swearing by the city of Jerusalem (since it’s God’s city) or by His earth, but evading their ultimate responsibility to Him. I believe it was to this cavalier culture that Jesus spoke when he said to stop making contracts altogether and simply live as honest and fair people.
Friend, don’t hide behind fancy words or pious promises. Instead, be a person who is completely resolved to live, walk, and speak the truth, even when risk is required. If you lose something because you were honest, God will see it and reward you. By choosing to honor Him before honoring men, you position yourself to receive showers of blessings from Heaven, and you open the door to greater intimacy with Him and with your fellow humans. Become a person of truth and you will inherit much more than you give up, as you cultivate influence that has eternal impact!