Why take a stance on homosexuality from Leviticus when we do not follow the washing and food laws?

One of the basic, very general rules of Biblical interpretation (a practice called “hermeneutics”) is that a teaching is considered valid if it is featured in both testaments. For instance, one of the reasons that Christians adhere to the Old Testament teachings of the Ten Commandments—first introduced in Exodus 20—is that they are repeated in various places throughout the New Testament (Christ Himself providing the great bulk of those references in the Gospels). If that is true, then the Biblical prohibition against homosexuality fits into that construction—while the prescriptions found in the hygiene and dietary laws ended the moment the curtain separating the Holy Place from the Holy of Holies in the temple in Jerusalem was torn in two upon the death of Christ on the cross (Matthew 27:51; Mark 15:38; Luke 23:45). From the Old Testament book of Leviticus we get these: (1) Do not lie with a man as one lies with a woman; that is detestable (literally, an “abomination”)—God speaking, Leviticus 18:22. This comes at the end of a long list of prohibitions against certain sexual behaviors which God condemns. God then explains why this practice, along with the others, are to be prohibited: Do not defile yourselves in any of these ways, because this is how the nations that I am going to drive out before you became defiled. Even the land was defiled; so I punished it for its sin, and the land vomited out its inhabitants. But you must keep my decrees and my laws. The native-born and the aliens living among you must not do any of these detestable things, for all these things were done by the people who lived in the land before you, and the land became defiled. And if you defile the land, it will vomit you out as it vomited out the nations that were before you. Everyone who does any of these detestable things—such persons must be cut off from their people. Keep my requirements and do not follow any of the detestable customs that were practiced before you came and do not defile yourselves with them. I am the Lord’”—God speaking, Leviticus 18:24-30. The second instance from Leviticus is similar: If a man lies with a man as one lies with a woman, both of them have done what is detestable. They must be put to death; their blood will be on their own heads—God speaking, Leviticus 20:13. Two important points from these two verses: First, it is God Himself speaking against the practice. He speaks against it because it offends Him. The Hebrew word is towebah (to-aw-baw^), which means an abomination, literally something disgusting or abhorrent. Let’s face it: God is the creator and designer of human sexuality, so He certainly has the right to speak out against its misuse. Second, it damages the ones doing it. The Hebrew word tame (taw-may^) comes from a root word which means “to be foul,” and it means to defile self, to pollute self, to make one’s self unclean or impure. The idea is an action which makes one contaminated or corrupted, especially in the eyes of God. The great damage is that it separates one from God, who rightly demands holiness in His people. Separation from God means that you are outside of relationship with Him—and there is nothing more damaging to a human being than that. The reward found in obedience is not the absence of judgment but rather the blessing and joy of relationship, knowing you are pleasing the Father. God’s anger at this sin (along with many others) was the impact it had on people with whom God wanted relationship, and His anger at how the sin of one could infect an entire group. The incredible judgment God imposed on the people of the land into which God brought the nation of Israel was that they had chosen as a population to embrace a lifestyle which included, among other things, homosexual practices—in direct violation to commands that He had communicated. They freely made their lifestyle choices completely contrary to God’s express word; that’s why they were punished so severely that their nations were literally destroyed out of existence. And obviously God’s command for both parties to such activity to “be put to death” (Leviticus 20:13) has a similar aim—to purge the sin completely out of the lives of the nation. Now, fast forward a whole bunch of centuries to the time of Paul, as that new thing called the “church” is trying to become established. As Paul writes to the church at Rome, he includes these words—very early on in that letter: The wrath of God is being revealed from heaven against all the godlessness and wickedness of men who suppress the truth by their wickedness, since what may be known about God is plain to them, because God has made it plain to them. For since the creation of the world God’s invisible qualities—his eternal power and divine nature—have been clearly seen, being understood from what has been made, so that men are without excuse. For although they knew God, they neither glorified him as God nor gave thanks to him, but their thinking became futile and their foolish hearts were darkened. Although they claimed to be wise, they became fools and exchanged the glory of the immortal God for images made to look like mortal man and birds and animals and reptiles. Therefore God gave them over in the sinful desires of their hearts to sexual impurity for the degrading of their bodies with one another. They exchanged the truth about God for a lie, and worshiped and served created things rather than the Creator—who is forever praised. Amen. Because of this, God gave them over to shameful lusts. Even their women exchanged natural relations for unnatural ones. In the same way the men also abandoned natural relations with women and were inflamed with lust for one another. Men committed indecent acts with other men, and received in themselves the due penalty for their perversion. Furthermore, since they did not think it worthwhile to retain the knowledge of God, he gave them over to a depraved mind, to do what ought not to be done. They have become filled with every kind of wickedness, evil, greed and depravity. They are full of envy, murder, strife, deceit and malice. They are gossips, slanderers, God-haters, insolent, arrogant and boastful; they invent ways of doing evil; they disobey their parents; they are senseless, faithless, heartless, ruthless. Although they know God’s righteous decree that those who do such things deserve death, they not only continue to do these very things but also approve of those who practice them—Paul, Romans 1:18-32. His words are absolutely consistent with Leviticus in the sense that they convey God’s great displeasure at the perversion done to His natural designs for our lives, and that the ultimate consequence is damage to the person themselves—the great damage of course being loss of opportunity to be a part of the Kingdom of God. That is the point Paul makes later to the church at Corinth, where he says in his first letter, Do you not know that the wicked will not inherit the kingdom of God? Do not be deceived: Neither the sexually immoral nor idolaters nor adulterers nor male prostitutes nor homosexual offenders nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God—Paul, I Corinthians 6:9-10.
What is so interesting though—and so reflective of the incredible love and grace of God—is that, though homosexuality is exposed throughout the Scriptures as sin, it is a sin from which we can be saved. Just after Paul wrote the verses shown above, he continued with these amazing words: And that is what some of you were (referring to the “sinners” in verses 9-10). But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God—Paul, I Corinthians 6:11. And it also reminds all of us that, once justified, completely saved from all our sins, we are then all called to the same standard—holiness. In other words, people saved from the sin of homosexuality are not then called to heterosexuality but rather to holiness. Listen to these wonderful words from the apostle Paul: Don’t you know that when you offer yourselves to someone to obey him as slaves, you are slaves to the one you obey—whether you are slaves to sin, which leads to death, or to obedience, which leads to righteousness? But thanks be to God that, though you used to be slaves to sin, you wholeheartedly obeyed the form of teaching to which you were entrusted. You have been set free from sin and have become slaves to righteousness. I put this in human terms because you are weak in your natural selves. Just as you used to offer the parts of your body in slavery to impurity and to ever-increasing wickedness, so now offer them in slavery to righteousness leading to holiness. When you were slaves to sin, you were free from the control of righteousness. What benefit did you reap at that time from the things you are now ashamed of? Those things result in death! But now that you have been set free from sin and have become slaves of God, the benefit you reap leads to holiness, and the result is eternal life. For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord—Romans 6:16-23. It is to holiness, to be holy because God is holy (verses in Leviticus 11:44-45, 19:2 and 20:7 that are quoted by Peter in I Peter 1:16). As Paul reiterated in his second letter to the church at Corinth, Since we have these promises, dear friends, let us purify ourselves from everything that contaminates body and spirit, perfecting holiness out of reverence for God—Paul, II Corinthians 7:1. As he reminded the Ephesian church, You were taught, with regard to your former way of life, to put off your old self, which is being corrupted by its deceitful desires; to be made new in the attitude of your minds; and to put on the new self, created to be like God in true righteousness and holiness—Paul, Ephesians 4:22-24. And as the writer of Hebrews likewise encouraged, Make every effort to live in peace with all men and to be holy; without holiness no one will see the Lord—Hebrews 12:14.