Thomas Aquinas Arguments For The Existence Of The Natural Law

The Natural Law
First used by ancient Greeks in their studies of morality, Natural Law could be considered as the backbone of all modern western civilization. The philosophy behind Natural Law demonstrates that humankind, as a species, knows certain things to be right and wrong, without any instruction. Humans know that many unjust things are wrong, it doesn't need to be taught, it is a universal truth known to all, with very few exceptions. The Natural law has long been subject to debate of where its true origin is, whether it be from a divine source, in God and His grace, or an earthly source, from the evolution of humanity. Wherever the Natural Law comes from, it seems to be a universal truth, known by all men and women from the first humans
The Natural Law has changed before, it even says so in the bible. The backbone of Natural Law is mankind’s universal morality, imbued within us from creation, however, in article five of St. Thomas Aquinas’ Summa Theologica, it gives biblical evidence of the Natural Law changing. Killing innocent people is one of the main arguments for the existence of Natural Law, and yet God commands Abraham to kill his own son, directly contradicting the sense of morality graced to Abraham, through the Natural Law in the first place.
Because it can change, the Natural Law must come from an ever-changing source, such as evolution, not God who, in the Old Testament, says: “For I am the Lord, I change not; therefore ye sons of Jacob are not consumed” (Malachi 3:6). God’s unchanging nature wouldn’t allow the Natural Law, which was prescribed by Him, to change over the course of time. It is unlike the nature of God to contradict itself, so when His nature goes against His own original teachings, it creates discrepancies in the origin story of the Natural Law from God’s grace.
Objection
v): "The Natural Law dates from the creation of the rational creature. It does not vary according to time, but remains unchangeable” (Papal Decretals)
“But this is the covenant that I will make with the house of Israel after those days, declares the Lord: I will put my law within them, and I will write it on their hearts. And I will be their God, and they shall be my people.” (Jeremiah 31:33)
Response to Objection 1:
The Natural Law must come from God, as it does not in fact change. The Natural Law is applied universally to each man, without distinction between one or the next. The mishaps in Natural Law come with the interpretation of Natural Law and the free will of man. Some groups or individuals, such as serial killers and radical Islamic terrorist groups still believe they are upholding the Natural Law. Part of the Natural Law is understood as meaning ‘it is not just to kill innocent people,’ but in the eyes of Islamic terrorists, people who betray Islam are no longer innocent. This may be the reason for their senseless killing of innocent men, women, and children, seemingly without remorse, and in direct discordance with the Natural Law, because they truly believe what they are doing is