A covenant is not just a promise before God, it is a promise like God’s, who has said He will never leave you nor forsake you.
A covenant is more than a contract. It does not protect our interests, as a contract does. It surrenders them. You come here to surrender yourself to the interests of each other, and you do this by making an oath. There is no mingling of blood, but a mingling of purpose as God himself makes you one flesh.