In the fifth chapter of Matthew we read Jesus' teachings on a wide variety of subjects. The chapter starts with a group of blessings that have been termed, The Beatitudes. Each beatitude begins with "Blessed are . . ." and then proceeds to teach some way of living that causes one to be blessed. The beatitude section is beautiful prose and profound.
In the rest of the chapter, Jesus covers a variety of topics. The topics include murder, adultery, divorce, vengeance, and showing love to those we hate. In one section of this chapter Jesus addresses the Law, meaning the Ten Commandments God gave to the people through Moses and other directives. Jesus proclaims that He has come to fulfill or complete the Law. Indeed with His death on the cross Jesus does fulfill the Law and ushers mankind into the age of grace.
One should notice in Jesus' teaching on the various topics that the standard He sets is higher, deeper, and more demanding than the Old Testament commands given. I submit two examples to illustrate my point. "Thou shalt not murder." is the sixth commandment. Jesus says in Matthew 5 if one is angry with their brother, and elsewhere if you hate your brother, then you have committed murder. He goes deeper than the actual act of physically taking another's life and add our attitude.
The other example is the seventh commandment. "Thou shalt not commit adultery." that is sexual relations with a married person who is not one's spouse. Jesus adds that if one has lust in their heart towards another than they have committed adultery in their heart. Again Jesus adds attitude or thought in addition to the actual physical act.
Jesus also taught on being truthful and letting your word stand on it's own. In verses 33 through 37 of Matthew chapter five, Jesus teaches that we should not undergird our word by swearing on something. The swearing here is not using the seven forbidden words as the Comedian George Carlin once waxed amusingly upon. Rather it is saying an oath by something recognized as greater than ourselves. Jesus teaches us to let our Yes mean Yes or our No, No. Another way of saying this is "Say what you mean, and mean what you say!" Be a person who stands by their word. As you live your life in this manner, others will soon learn your word can be trusted. Being recognized as a person of one's word is a valuable, and rare, commodity.
Jesus expands His teaching on standing by one's word in Matthew 21:28-32. In this passage Jesus shares a parable about two sons. The father tells his sons to go work in the vineyard. One son says "No," and the other son says, "Yes." The son who answered "Yes," is the obedient son, right? As the parable continues we find that the son who readily replied, "Yes," or more exactly, "I will, sir." Did not do as he said he would. The son who said no, and I'm sure at the time disappointed if not angered his father, changed his mind and went to the field to work. Jesus puts forth the question, "Who did what his father wanted." To which those present answered correctly, "The first," that is the one who said no but then relented and obeyed.
Jesus used this parable to teach that there are people in the world who say "No" to God's ways but later repent and embrace Him and obey. There are also those who either by zealous exuberance, or a desire to curry favor immediately say yes but then fail to follow through or who perhaps had no intention of ever obeying. Jesus teaches it is the one who ultimately obeys who is in the right. Appearance means nothing, obedient action, even if one initially refuses, is rewarded. This passage is another example of saying what you mean and meaning what you say, however, if you say "No" but change your mind and obey, then you are forgiven and rewarded.
We must be people of our word; in our word to man but definitely in our word to God. "Do not be deceived, God cannot be mocked. A man reaps what he sows." Galatians 6:7