Matthew 5:37 says - "But let your 'Yes' be 'Yes,' and your 'No,' 'No.' For whatever is more than these is from the evil one" (cf. James 5:12). Jesus' concluding point is a powerful one. Instead of making oaths, one would be better off simply living in such a way that whatever he states will be accepted as the truth. His character and life should confirm the truthfulness of his words so that no oath is necessary. A righteous man should be content making a sincere affirmation or denial of any statement, and others should be satisfied to take such a statement at face value.
Many who study this passage naturally reflect upon certain oaths that are commonly made today, and they wonder: Is it wrong to affirm a judicial oath, for example, or exchange marital vows? I believe the answer is "no." Allow me to explain why.
It is common in wedding ceremonies for couples to pledge their love and faithfulness to each other, but these vows simply explain the extent of the "Yes, I will be your husband or wife" affirmation. Marriage vows are promises that do not require one to swear or make an oath upon a higher being or thing.
In a judicial setting, however, there are times where one is required to swear or make an oath. Although such should not be necessary for a Christian, it appears that complying with such is not wrong. Jesus Himself answered under oath before the Sanhedrin (Matt. 26:63,64). Were His words any more truthful under oath? Of course not, but Jesus didn't resist the authority of the high priest in this regard. Thus, it would be difficult to conclude that we should resist the authority of our government in judicial proceedings. Paul also made oaths on certain occasions. They seem to center around the notion that God was a witness to the truthfulness of the apostle's statements (e.g., Rom. 1:9; II Cor. 1:23; Gal. 1:20; Phil. 1:8). Therefore, it would seem to be acceptable for one to use such language today for emphasis. The examples of Jesus and Paul strongly indicate that the words of the Lord in Matthew 5:33-37 should not be interpreted in an absolute sense. The thrust of the teaching is to correct the abuses of oaths common among men, not to forbid every type of oath.
Ultimately, God wants you to be a person of your word. Your word should be your bond. You should not feel a need to voluntarily make an oath. You should not feel a need to say, "I promise." A simple "yes" or "no" ought to be sufficient. When you affirm that you will do something, do it! Stick by your word regardless of the cost to yourself (Psa. 15:4). The only exception to this would be if your words would end up forcing you to commit sin. In that case, you should break your word and seek forgiveness for making such a foolish promise to begin with.
Furthermore, when you do not want to do something--or simply cannot--then declare such plainly. Don't say "maybe" when you know the answer is "no." Don't say "yes" when you do not mean it. When you give your word, regardless of the situation, people are listening and watching to see if you mean what you say. It is difficult to trust a person when his words do not harmonize with his actions. Friends, let us always mean what we say! It is better to say nothing than to lie (cf. Matt. 12:36,37), but the best course of action by far is to speak the truth plainly and be a man or woman of your word.