God is absolutely pure, holy, and righteous.  Therefore, His moral law is also pure, holy, and righteous because it is a reflection of His character.  But, a question arises.  If God is absolute and unchanging, why would He change various laws regarding such things as not eating pork (Deut. 14:3,8) and not wearing clothes made with two kinds of material (Deut. 22:11)?  After all, these things are not taught in the New Testament.  The answer is simple.  Not eating pork and not wearing clothes woven of two kinds of material are not moral issues.  Instead, they are commands aimed at ancient Israel as examples of cultural and spiritual separation from the unbelieving world. Lying, stealing, homosexuality, bestiality, etc., are issues of morality that deal with all people, everywhere.  Let me show you.

For Israel Only	The sins of the nations
Lev. 12:1-3, Then the Lord spoke to Moses, saying, 2 “Speak to the sons of Israel, saying, ‘When a woman gives birth and bears a male child, then she shall be unclean for seven days, as in the days of her menstruation she shall be unclean. 3 And on the eighth day the flesh of his foreskin shall be circumcised.'”	Lev. 20:23, “Moreover, you shall not follow the customs of the nation which I shall drive out before you, for they did all these things, and therefore I have abhorred them.”
Num. 15:38, “Speak to the sons of Israel, and tell them that they shall make for themselves tassels on the corners of their garments throughout their generations and that they shall put on the tassel of each corner a cord of blue.  39 “And it shall be a tassel for you to look at and remember all the commandments of the Lord, so as to do them and not follow after your own heart and your own eyes, after which you played the harlot,	Lev. 18:20; 20:10, don’t have intercourse with your neighbor’s wife
Deut. 14:3,8, “You shall not eat any detestable thing… 8 “And the pig, because it divides the hoof but does not chew the cud, it is unclean for you. You shall not eat any of their flesh nor touch their carcasses.”	Lev. 18:22, don’t lie with a male as with a female
Deut. 22:11, “You shall not wear a material mixed of wool and linen together.	Lev. 20:15, don’t lie with animals

We see in the table above in Leviticus 12:1-3 that God is speaking only to Israel when He talks about uncleanness and circumcision.  Circumcision, for example, was not something proclaimed to everyone by God.  It was only to Israel.  If God’s moral character requires circumcision (which is a covenant sign only for the people of Israel), then why didn’t God require it of everyone?  The reason is that it was not a universal ceremonial requirement for all people.  However, the moral requirements of honesty, fidelity, and sexual purity are for everyone.

There is an important concept to explain here.  The Old Testament points to Jesus in the New Testament.  The Old Testament has types and shadows of the reality found in the person and work of Christ (Romans 5:14; Col. 2:16-17; Heb. 10:1; 11:19).  Therefore, physical circumcision (Lev. 12:3, cited above) was representative of the true circumcision of the heart which was spoken of in the New Testament (Romans 2:29), a circumcision that occurs with faith in Christ.  In the same way, those things in the Old Testament (dress codes, eating codes, etc.) are types and shadows of the things found in the New Testament.  Let’s take a look at the other verses listed above.

In Numbers 15:38-39, God is addressing Israel.  He speaks about having tassels on the corners of the garments.  These tassels represented the Law of God (Nu. 15:39) which was formally given only to Israel (Exodus 34:27; 34:1-35).  The tassels, though part of the Law, were not a moral issue.  They were a ceremonial issue, and they were for Israel only.  Likewise, we see in Deuteronomy 14:1 that God says, “You are the sons of the Lord your God; you shall not cut yourselves nor shave your forehead for the sake of the dead. 2 For you are a holy people to the Lord your God; and the Lord has chosen you to be a people for His own possession out of all the peoples who are on the face of the earth.”  Obviously, He is addressing things like not eating pork only to the people of Israel and not the Egyptians, Assyrians, etc.  In the same way, the context of Deuteronomy 22 is an address not to the whole world but to those people who dwell “in the land which the Lord your God gives you to possess,” (Deuteronomy 21:1).  Instructions are given to the priests of Israel and the elders on what to do in certain circumstances, including what to do when they found a dead body (21:3), went to battle (22:10-14), carried out capital punishment (21:22), how to not defile “the land which the Lord your God gives you as an inheritance,” (Deuteronomy 21:23), what to do when their countrymen’s cattle go astray (22:1-4), gender separation and clothing (22:5), not selling two kinds of seed in the Vineyard (Deuteronomy 22:9), etc.  These commands, and others within the text, are addressed to the Jews only.  But also notice that in the table above in the right column, we see there are certain admonitions that God addresses regarding the sins of the nations around Israel, such as adultery, homosexuality, and bestiality.  So, He covers both: things addressed to Israel, and things addressed to all nations.

The reason there is a difference between Israel and all the other nations is that Israel was chosen by God to be set apart for His holy use (Deuteronomy 7:6).  Therefore, the purity requirements of eating and dressing were typological of the holiness that God requires of His people, as well as their calling to be separate from the world.  They were to be separate from the world.

Think about the sacrificial system which God instituted for Israel (not all the nations), where Israel would sacrifice bulls and goats for the cleansing of their sins.  Obviously, this morally significant practice in the Law was intended only for Israel.  Those sacrifices ultimately pointed ahead to the real sacrifice of Jesus (1 Peter 2:24) since they were a shadow of the real sacrifice (Hebrews 10:1).  The same goes for eating, dressing, and worship codes.  This is a common theme in biblical theology (see the typology between Abraham and Isaac as they relate to God the Father and Jesus).  The sacrificial system was not instituted for all nations.  However, a sacrifice was provided for all nations later on by Christ when he died on the cross (Matthew 15:24; 1John 2:2).  Therefore, the sacrificial system of ancient Israel was for them only and was representative of the true sacrifice to come later, the sacrifice of Christ.

So, God is not changing all His laws.  Instead, He has established some to be valid only to Israel (not eating pork, rest on the Sabbath, etc.) and others for everyone (don’t lie, don’t steal, don’t murder, etc.).  There is no contradiction between His unchanging nature and how He works with different people groups at different times.  All you have to do is read the context to find out.