God is entirely simpleGod is entirely simple (not composed of parts), and God is immutableGod is immutable. God does not change in time; God is not in time; nothing about God changes.
If this is so, how can God, for example, prohibit the Jews from eating pork before Christ, yet after Christ God allows those Jews who converted to Christianity to do so? Christians believe the God of the Old Testament and the New Testament is the same, one God.
There are three kinds of lawthree kinds of law, forming a hierarchy: eternaleternal, naturalnatural, and humanhuman.
There are three types of precepts of the Old Lawthree types of precepts of the Old Law: moralmoral, ceremonialceremonial, and juridicaljuridical. The latter two were meant to prepare the Jews for Christ, and they ceased to bind after Christ, but the moral laws (natural lawnatural law) are forever binding.
A very relevant question is [whether natural law can change][11]. If it can, then what is religiously valued centuries ago (like that marriage is between one man and one woman) is not necessarily so today. This is moral relativism.
However, as is said in the Decretals (Dist. v): "The natural law dates from the creation of the rational creature. It does not vary according to time, but remains unchangeable."
So, since humans today are of the same species or nature as our ancestors, the natural law for us is the same as it was for them.
Note: In everything below the horizontal line I am only considering moral values. Dogmatic truths, which could be considered "values" in a broader sense, are immutable because God cannot contradict himself. The "values" upheld by the eternal, divine law are immutable because, by definition, the divine law is eternal, participating in God's eternally unchanging nature: "every knowledge of truth is a kind of reflection and participation of the eternal law, which is the unchangeable truth," as Augustine says in De Vera Relig. xxxi (sourcesource).