Although modern-day covenants have spiritual undertones, in Bible times they were simply formal agreements between two parties. Individuals, families, or nations could enter into covenants for a variety of reasons, but most often for protection of some sort. In ancient Palestine, with such a large number of people groups in a relatively small area, political covenants were common to defend against neighboring powers. 

In some cases, the respective parties were equals, often referred to as "brothers" in the covenant contract. In such a parity treaty, the members stood united against a common enemy. If one was threatened, the others would come to the rescue. More commonly, however, was a suzerain/vassal treaty between nations of unequal size and strength, where a superpower (suzerain) would invite or force smaller nations (vassals) into alliance. In the covenant contract, the partners were often referred to as "father and son" or "lord and servant", emphasizing the power imbalance. The vassal was responsible for paying tribute (money, food, livestock) and supplying military assistance when the suzerain went to war. In return, the suzerain was responsible for military protection. Although a suzerain could have multiple vassals, a vassal could only make a covenant with one other suzerain. 

Ancient covenants employed common terms within the contract itself. Making such a treaty was to "cut a covenant" - the "cutting" referred to the slaying of a sacrificial animal. During the ceremony, the vassal was sometimes required to walk between the severed parts of the sacrifice, which served as a vivid reminder of what would happen if they broke the covenant. The Hebrew word for adhering or honoring a covenant was hesed. Showing loyalty or covenant faithfulness was to "love" the suzerain, while betrayal was considered an act of "hate". If the covenant stipulations were met, a vassal could expect "blessings", while "curses" would come their way if they rebelled.

In keeping with the custom of the time, covenants occur frequently in the Bible. When Abraham’s and Lot’s flocks became too large to live alongside each other, they parted ways after making a parity treaty of mutual protection. Before long, Lot and his household were captured by an invading army, so Abraham mustered his men and rescued him from captivity (Genesis 13-14). During the conquest of Canaan, the people of Gibeon tricked Israel into making a covenant with them. However, when Gibeon’s neighbors, with whom they were presumably allied before Israel, retaliated by attacking them, Israel was compelled to protect their new vassal (Joshua 9-10). And when Israel was threatened with Assyrian invasion, a prophet warned against alliance with Egypt, citing that God should be their only suzerain (Isaiah 31).

Covenants are a major theme in God’s dealings with humanity. The divine covenants recorded in the Bible use the same wording as the social covenants of the day. For example, Israel was to have no other suzerains besides God (“no other gods”); there were blessings/curses for following/rejecting his laws; God refers to himself as “Lord” and “Father”, while Israel is called his “servant” and “son”; covenant faithfulness (hesed) is emphasized frequently. There are five major covenants between God and men recorded in the Old Testament.

The ground is cursed because of you. You’ll eat from it in pain all the days of your life. Thorns and weeds will grow for you and you’ll eat plants from the field. You’ll eat bread by the sweat of your face until you return to the ground, because you were taken from it. You are dust and you’ll return to the dust.  – Genesis 3:17-19

God said, “This is the sign of the covenant that I’m making between me and you and every living soul that is with you for perpetual generations: I’ve put my bow in the cloud, and it will be a sign of the covenant between me and the earth. When I bring a cloud over the earth, and the bow is seen in the cloud, I will remember my covenant… and the waters will never again become a flood to destroy every body.”  – Genesis 9:12-15

The Lord told Abram, “Go from your country, your relatives, and your father’s house, to the land I’ll show you. I’ll make you a great nation. I’ll bless you and make your name great, and then you’ll be a blessing. I’ll bless those who bless you and curse those who curse you. And all the families on earth will be blessed through you.”  – Genesis 12:2-3 

You shall be my own possession among all the peoples, for all the earth is mine. And you shall be a kingdom of priests to me, and a holy nation.  – Exodos 19:5-6

Moses wrote down all of the words of the LORD. Then he got up early in the morning and built an altar under the mountain with twelve pillars for Israel’s twelve tribes. He sent boys from Israel’s sons and they brought up offerings and sacrificed bulls for peace to the LORD. Moses took half of the blood and put it in bowls, and scattered the other half of the blood on the altar. Then he took the book of the covenant and read it in the people’s ears, and they said, “We will do and hear everything the LORD has said!” So Moses took the blood and scattered it on the people, saying, “Look, the blood of the covenant, which the Lord has made with you upon all these words.”  – Exodus 24:4-8

I will raise up your seed after you, who will come from your bowels, and I will establish his kingdom. He will build a house for my name and I will establish the throne of his kingdom forever. – 2 Sam 7:12-13

Jeremiah is the only Old Testament writer that mentions a new covenant, which is where the term “New Testament” comes from. The writer of Hebrews quotes Jeremiah’s words regarding this new covenant in the largest single citation of Old Testament text within the New Testament. 

“Look, the days are coming,” the LORD announces, “when I’ll make a new covenant with Israel’s house and Judah’s house, unlike the covenant I made with their fathers in the day I took their hand to bring them from the land of Egypt – my covenant that they broke, even though I was their husband,” the LORD announces. “However, this is the covenant I’ll make with Israel’s house after those days,” the LORD announces. “I’ll put my law inside them and I’ll write it on their hearts. I’ll be their God and they’ll be my people. They won’t teach anymore, a man to his neighbor and a man to his brother, saying, ‘Know the LORD,’ because they’ll all know me, from the smallest to the greatest,” the LORD announces, “because I’ll forgive their guilt and not remember their sin anymore.”  – Jeremiah 31:31-34

If the first [covenant] had been faultless, there wouldn’t have been any place to look for a second. But fault was found…. And when he said, “new,” he made the first old, and the old and aging have nearly disappeared.  – Hebrews 8:7-8,13