How would you respond to the following statement:
If you’re going to use Leviticus 18:22 to say that homosexuality is a sin, then you must not plant your field with two types of seed or eat any beef (Leviticus 19:26) or wear clothing made from more than one type of material (Leviticus 19:19).

     A person using this argument doesn’t understand why the Law was given, who it was given to and when parts of it were to expire.

     Why was the Old Testament Law given? The Jews had just endured over 400 years of slavery doing nothing but making bricks. That’s almost twice as long as the USA has existed as a nation. They had no idea how to survive on their own. They knew nothing of farming, forming & running a government, setting up a legal code, etc. The Law gave them very detailed instructions on how to do all of this. It was also used to identify and preserve the geneaological line that the Messiah was to come from. It explained in many scriptures who the Messiah would be and why He had to come. It foreshadowed His coming. The dietary laws were to prevent food-born illnesses. Many of the ritual laws were given for safety and cleanliness. The farming laws provided for their sustenance.

     Who was the Law given to?  The Jews and the Jews only (Exodus 19:5,6).

     What parts of the Law were temporary and what parts were permanent? There were several parts to the Law. The parts that foreshadowed the Messiah were fulfilled at His 1^st coming. The civil & legal laws were needed for Israel to function as an independent country. These laws ceased to exist when Israel was conquered by a foreign nation. The legal punishments are harsh by today’s standards. But God meets us where we’re at, not where we should be. These laws were very much in line with the laws of the surrounding nations at the time. The BIG difference is that they were more redemptive in nature and served to protect the victims whereas the surrounding countries laws were harsher and meant to protect the rich and elite over the common person. But we can learn from these laws that God loves and protects us while meeting us where we’re at, not where we should be. The only laws that directly transfer are the moral laws.

     The moral laws (but not their punishments) don’t change because God doesn’t change. He is the same yesterday, today and forever (Hebrews 13:8). That is why the moral laws of Leviticus 18, 19 and other places still apply today but the other types don’t (Leviticus 19:19-23, 27, 28, etc.) Unfortunately, the laws were all bunched together, so it falls to us to sort them out.

     Further comments on the Old Testament Law:
All of Israel’s laws were designed to be a blessing to them (Leviticus 26:3-13).

     Laws that begin with “do” or “do not” are what we call apodictic laws. They are direct commands. These laws are paradigmatic (examples rather than exhaustive lists meant to cover every situation). If you were to try to obey these laws, they would show you how impossible it is to please God on your own. Compared to all the Old Testament laws, they are in the minority.

     Laws that are on a case-by-case basis are called cauistic laws. An example of where these laws apply is Deuteronomy 15:12-17. If you aren’t an Israelite and do  not own slaves, this law doesn’t apply to you. These cauistic laws constitute a large portion of the over 600 Old Testament laws. None of them are renewed in the New Testament. Because these laws apply to Israel’s civil, religious and ethical life, they are limited in their applicability and do not apply to Christians today.

     Some usual laws;
“Do not cook a young goat in its mother’s milk” (Deuteronomy 14:21) or “Do not mate different kinds of animals” and “Do not wear clothing woven of two different kinds of materials” (Leviticus 19:19). What the heck is wrong with that you may ask?
In Deuteronomy 14:21, this and other prohibitions were designed to forbid the Jews from engaging in the fertility cult practices of the Canaanites. They thought that by boiling a kid goat in its mother’s milk that it would magically ensure the continuing fertility of their flock.
In Leviticus 19:19, the Canaanites thought that by mixing animal breeds or different seeds or materials that it would “marry” them together so as to magically produce a bountiful harvest or herd. God did not want the Israelites to be tainted with any of the Canaanites practices. Many of their practices were of a pornographic/orgiastic/sexual nature. If the Israelites were to remain pure and committed to following God’s will for their lives, they were to avoid all of these Canaanite practices.

Book references:
“How to Read the Bible for all its Worth” by Gordon Fee & Douglas Stuart, chapter 9
“Jesus is involved in politics” by Neil Mammen, chapter 20