When we think of an oath, we can readily think of an oath to uphold an office like an elected official or a peace officer. We can also think of the oath to tell the truth when giving testimony in court. This oath used to be done with the right hand placed on the Bible to remind people of the seriousness of the oath, and that their testimony was not just before men, but God Himself. One of the most important oaths one can take is the marriage vow. The familiar phrases "A man is only as good as his word" and "A man's word is his bond" illustrate the need to keep oaths. When people purposely don't keep their promises, there is a breakdown in trust and credibility which is the basis of all relationships. Although the Gibeonites deceived Joshua into an oath, he still felt obligated to uphold what he promised (Josh 9). David asked, "LORD, who shall abide in thy tabernacle? who shall dwell in thy holy hill (Ps 15)?" Part of the answer is, "He that sweareth to his own hurt, and changeth not." God used the faithfulness of the Rechabites to the oath of their ancestor as an illustration of His faithfulness to Israel and their unfaithfulness to Him (Jer 35).
People not only make promises to each other, they make them to God. A classic example is something to the effect, "God, if you get me out of this I will do want you want." People should be very careful about what they promise to God, because He takes it seriously (Ecc 5:1-7). It is better to not make a promise we will not keep and rely on the grace of God than to not keep the promise, especially after God has kept His part of the deal (Mt 5:33-37, Jam 5:12). It is wise to not make deals with God, but rather to pray for His help and trust in His will. This is not to say we should not have a commitment to serve God generally.
This may seem backwards, but God makes oaths to man. To sware in the Bible literally means "to seven one's self" because the number seven represents completion and fulfillment. It means that to sware to do something is serious and demands faithful fulfillment. The Bible mentions in 55 verses that God swore to Abraham and his descendants that they would be given the land of Canaan. The Bible also calls this promise of God an oath 6 times. There are other oaths of God mentioned in the Bible:
1. The covenant of Moses (Deut 29:12 & 14, Eze 16:8 & 59-60, Dan 9:11)
2. The covenant of David (2Sam 7, Ps 89:49, Acts 2:30)
3. The oath to the priesthood of Melchizedek (Ps 110:4, Heb 7:21)
The words sware, oath, promise and covenant are closely related. The original meaning of covenant is "a cutting" because one way people would seal the most serious covenants was with blood. They would cut animals in half, lay the two halves on the ground, and both parties would pass through the pieces to symbolize the binding oath they had joined together in. This is what happened with God and Abraham in Genesis 15. Covenant also means confederacy, alliance, treaty, or pledge. What a thought that God would bind Himself to man in such a way!
Yet God took this to even another level. He did not just bind Himself with an oath to man with the blood of animals. He manifested Himself in the flesh, became one of His own creation, shed His blood, an died for us (Mt 26:28, Acts 20:28, Heb 8-10). We can enter into a holy blood covenant with God by being baptized by immersion in water in the name of Jesus Christ for the remission of sins (Acts 2:38, Acts 10:43-48, Acts 19:1-7, Acts 22:16). This is the New Testament version of "passing through the pieces" and entering into a blood oath with God Himself. God already gave Himself for us. He has committed Himself to us through the covenant. He now calls us to join Him and make our commitment to Him.
Man is not always faithful, but God is. Hebrews 6 discusses the faithfulness of man compared to the faithfulness of God. Verses 1-12 describe the faithfulness of man and our need to do better. Verses 13-20 describe the faithfulness of God, and how it is impossible for Him to do better. Men usually make oaths based on something higher than themselves. There is no one higher than God, so when He makes an oath, He can do no better than to base it on Himself. He never fails. He is perfectly faithful. When men make an oath to each other, that settles the matter. How much more when it is God making the oath? Yet God was so willing to abundantly show how unchangeable His promise to us is that He confirmed it by two things. Although God is almighty, and nothing is too hard for Him, one thing He cannot do is lie. Therefore the hope we can have in Him is certain, firm, and of force. Philippians 1:7 uses the same word as Hebrews 6:16 to describe the surety of the gospel of Jesus Christ.
We get disappointed by people, and we fail ourselves. When this happens often or very deeply, we tend to struggle with trusting God. He is not a man, and does not fail (Num 23:19, 1Sam 15:29). We can be absolutely confident that He will keep His oath to us. We need to settle that in our faith and focus on the real issue - will we be faithful?