An understanding of the word “covenant” is essential to understanding the relationship between God and man. In the secular world, a covenant is like a contract, in that it is a binding agreement between two or more parties, characterized by the obligations imposed on each and the benefits that each will receive. It is the result of discussion, negotiation, and compromise. It is a lateral agreement in the sense that all involved parties are of the same station in the order of creation; in other words, they are equals.
The Covenant between God and man, in contrast, is between unequals. It is a vertical contract, and its terms are dictated by God. Discussion, negotiation, and compromise have no role in its establishment. God needs nothing from us: although the relationship is vertical, it is we who benefit. The Universal House of Justice explains, “ A Covenant in the religious sense is a binding agreement between God and man,whereby God requires of man certain behaviour in return for which He guarantees certain blessings, or whereby He gives man certain bounties in return for which He takes from those who accept them an undertaking to behave in a certain way.”  The terms of the contract flow in one direction only – from God to man.
There are two kinds of Divine Covenant. The Greater Covenant is the assurance that God will successively send Manifestations to guide mankind, and obligates us to recognize and follow Them, in return for which we receive blessings from God. The Lesser Covenant is the covenant that each “… Manifestation of God makes with His followers that they will accept His appointed successor after Him. … It is a Covenant of this kind that Bahá’u’lláh made with His followers regarding ‘Abdu’l-Bahá and that ‘Abdu’l-Bahá perpetuated through the Administrative Order…” 
It is the Greater Covenant that Bahá’u’lláh describes in the first paragraph of the Kitab-i-Aqdas: “The first duty prescribed by God for His servants is the recognition of Him Who is the Day Spring of His Revelation and the Fountain of His laws, Who representeth the Godhead in both the Kingdom of His Cause and the world of creation. … It behoveth every one who reacheth this most sublime station, this summit of transcendent glory, to observe every ordinance of Him Who is the Desire of the world. These twin duties are inseparable. Neither is acceptable without the other….” 
Obedience and law are intimately connected, of course, and an aspect of Baha’i Law can be understood by applying the principle of the harmony of science and religion. The Universal House of Justice writes, “Just as there are laws governing our physical lives…, so also there are laws governing our spiritual lives. These laws are revealed to mankind in each age by the Manifestation of God, and obedience to them is of vital importance…” 
Physical laws, the laws of science, are descriptive rather than prescriptive: no one passes a law decreeing gravity, for example. Gravity is woven into the very fabric of the universe, and the “Law of Gravity” describes how it works. We obey it to our benefit and ignore it at our peril. No reasonable person tries to repeal the law of gravity because it “just is”; it doesn’t care whether we like it or not, and it isn’t going to change to suit our preferences. Physical laws describe the structure and dynamics of the material universe – they tell us how it works.
Likewise, “there are laws governing our spiritual lives”, which are revealed by God’s Manifestations. They are built into the very fabric of the spiritual universe; and Revelation tells us how they work – the underlying laws of the spirit are reflected by Divine Laws and Principles. In that sense, physical law and spiritual law are analogous.
We see physical law and spiritual law as being different because, in the heirarchy of existence, we stand between the material and the spiritual. We are above the material, so we can discover its laws. We are below the spiritual: the spiritual surrounds use, and that which is surrounded cannot understand that which surrounds. Therefore, the structure of the spiritual universe has to be explained to us – the Manifestation has to give it to us as Revelation. Because it is revealed rather than discovered, it can be perceived as arbitrary and changeable, but in reality it is neither. It controls our spirits just as physical law controls our bodies. The misconception that Revealed Laws are arbitrary becomes a source of opposition.
 (23 March 1975, from a letter written by the Universal House of Justice to an individual believer)
 The Kitab-i-Aqdas by Baha’u’llah.
 Letter from the Universal House of Justice, dated February 6, 1973, to all National Spiritual Assemblies, in Messages from the Universal House of Justice, 1963-1986: The Third Epoch of the Formative Age, par. 126.2