The Bible establishes up front God's basic design for marriage and human sexuality, and the biblical authors make clear that anything outside of that God-designed union of man and woman in permanent matrimony is sinful. Thus, even if homosexuality went entirely unmentioned in the Bible, the clear sexual ethic that runs through the Scriptures from beginning to end would exclude homosexual practice and make it clear that such acts are sinful. The Bible does go further and explicitly identifies homosexuality as a sin in several places, so this is not merely an inference or deduction, but the focus throughout Scripture is on a positive picture of a specific design for sex between a man and a woman within a committed marriage as God's design which we cannot step outside without sin.
Marriage and Sexuality
Sexual morality is an important topic throughout the Bible, and its basis was established in creation itself. At the beginning of Genesis we are told:
"Then God said, 'Let Us make man in Our image, according to Our likeness; and let them rule over the fish of the sea and over the birds of the sky and over the cattle and over all the earth, and over every creeping thing that creeps on the earth.' God created man in His own image, in the image of God He created him; male and female He created them. God blessed them; and God said to them, 'Be fruitful and multiply, and fill the earth, and subdue it; and rule over the fish of the sea and over the birds of the sky and over every living thing that moves on the earth,'" (Genesis 1:26-28).
So, God made humanity uniquely in His own image. He granted them a special purpose and position of governance, giving them dominion over the earth and all its fullness. He made them male and female and bid them to be fruitful and multiply, thus ordaining and blessing sexuality as a positive good, a procreative act between men and women. This theme is developed more in the second chapter:
"For this reason a man shall leave his father and his mother, and be joined to his wife; and they shall become one flesh. And the man and his wife were both naked and were not ashamed," (Genesis 2:24-25).
Father and mother. Husband and wife. Two becoming one flesh. Naked without shame. This is God's beautiful design for marriage and sexuality. Indeed, the very story of Genesis 2 communicates this wonderfully. Eve made from the rib of Adam, bone of his bone and flesh of his flesh. Woman and man literally a part of one another. Man is incomplete and imperfect without woman. Woman is made from man as is God's ultimate gift to man. The two are equally made in the image of God and share dominion over creation, yet each is distinct and completes the other. Together they can make life and complete the purpose God has for humanity. This is God's design, and it is a masterpiece of beauty. To reject it and conceive of our own sexual vision is to blaspheme the designer and profane the gift. This is the standard that runs through all of Scripture and the foundation for biblical sexual morality.
Jesus Himself reminded people of this. When they challenged Him on divorce, He did more than just tell them the right answer to the question. He reminded them that God established sex and marriage long before Moses and that the standard goes back to the beginning.
"Some Pharisees came to Jesus, testing Him and asking, 'Is it lawful for a man to divorce his wife for any reason at all?' And He answered and said, 'Have you not read that He who created them from the beginning made them male and female, and said, "For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh"? So they are no longer two, but one flesh. What therefore God has joined together, let no man separate,'" (Matthew 19:3-6).
Some try to object that, since Jesus was addressing a question about divorce, the logic He uses here must, therefore, be restricted only to that question. That somehow the overtly stated supremacy and standard of what God designed in marriage from the beginning can have no other implications, but this is absurd. If a mother warns her son not to touch the stove because it is way too hot and things that hot will burn you, it is perfectly legitimate for him to deduce that he should also keep his hands back from a fire for the same reason. If things that hot burn you, then it doesn't apply only to stoves. If the basis of Marriage and sexuality is what God joined together in the beginning, the implications are clear and broad. A man, if he is to be sexually active, must marry a woman and be sacredly devoted to her. The conclusion of the conversation is telling:
"The disciples said to Him, 'If the relationship of the man with his wife is like this, it is better not to marry.' But He said to them, 'Not all men can accept this statement, but only those to whom it has been given. For there are eunuchs who were born that way from their mother’s womb; and there are eunuchs who were made eunuchs by men; and there are also eunuchs who made themselves eunuchs for the sake of the kingdom of heaven. He who is able to accept this, let him accept it," (Matthew 19:10-12).
Wholly devoted marriage to a woman or complete chastity are the only options a man has. Anything else is sin. As Paul notes:
"For this is the will of God, your sanctification; that is, that you abstain from sexual immorality; that each of you know how to possess his own vessel in sanctification and honor, not in lustful passion, like the Gentiles who do not know God," (1 Thessalonians 4).
All of this, of necessity, rules out homosexuality.
God's Moral Law and Homosexuality
In the law of Moses, there are very explicit statements about the immorality and sinfulness of homosexuality. For example, we read:
"You shall not lie with a male as one lies with a female; it is an abomination," (Leviticus 18:22).
This is not simply one of the distinctive holiness commands by which Israel was to set themselves apart from other nations as a special people, like dietary laws and such. This is a moral law by which all nations are judged before God. The list of primarily sexual sins in Leviticus 18 that contains this command ends with the statement:
"Do not defile yourselves by any of these things; for by all these the nations which I am casting out before you have become defiled. For the land has become defiled, therefore I have brought its punishment upon it, so the land has spewed out its inhabitants," (Leviticus 18:34-25).
The nations were not punished for eating pork, wearing mixed fabric, or even working on the Sabbath. Such commands were distinctive to maintaining Israel as a sacred people. The nations were judged, however, for breaking universal moral laws of God like sexual immorality, including homosexuality. Now, some have suggested that this is meant specifically to address ancient homosexual temple prostitution as it related to the worship of false gods, but that is not how Leviticus treats it. Note in chapter 20 we read again:
"If there is a man who lies with a male as those who lie with a woman, both of them have committed a detestable act; they shall surely be put to death. Their bloodguiltiness is upon them," (Leviticus 20:13).
But this is not in a section about cultic practices. Note the verses just before:
"If there is a man who commits adultery with another man’s wife, one who commits adultery with his friend’s wife, the adulterer and the adulteress shall surely be put to death. If there is a man who lies with his father’s wife, he has uncovered his father’s nakedness; both of them shall surely be put to death, their bloodguiltiness is upon them. If there is a man who lies with his daughter-in-law, both of them shall surely be put to death; they have committed incest, their bloodguiltiness is upon them," (Leviticus 20:10-12)
And just after:
"If there is a man who marries a woman and her mother, it is immorality; both he and they shall be burned with fire, so that there will be no immorality in your midst," (Leviticus 20:14).
This is about consensual, interpersonal, sexual acts. It's not about idolatry. A man is not to have sex with another man for the same reason he is not to commit adultery or incest. And again, we are told that the other nations were judged for these very things and that this is why God abhorred the Canaanite nations, (Leviticus 20:22-23). Thus, the precepts against homosexuality (and all sexual immorality) are not limited to Old Testament Israel. They are a standard by which God judges all the peoples of the world.
The New Testament and Homosexuality
The standard does not change in the New Testament. The New Covenant writings uphold the same clear sexual morality for the same reasons, and they explicitly point out Homosexuality as a sinful deviation from it. To the church in Rome, Paul takes the issue, again, right back to the beginning.
"For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men who suppress the truth in unrighteousness, because that which is known about God is evident within them; for God made it evident to them. For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse. For even though they knew God, they did not honor Him as God or give thanks, but they became futile in their speculations, and their foolish heart was darkened. Professing to be wise, they became fools, and exchanged the glory of the incorruptible God for an image in the form of corruptible man and of birds and four-footed animals and crawling creatures. Therefore God gave them over in the lusts of their hearts to impurity, so that their bodies would be dishonored among them. For they exchanged the truth of God for a lie, and worshiped and served the creature rather than the Creator, who is blessed forever. Amen," (Romans 1:18-25).
Creation, the fall, the dawn of human sinfulness and the origin of our idolatries and immorality are all first summarized. What is the result?
"For this reason God gave them over to degrading passions; for their women exchanged the natural function for that which is unnatural, and in the same way also the men abandoned the natural function of the woman and burned in their desire toward one another, men with men committing indecent acts and receiving in their own persons the due penalty of their error. And just as they did not see fit to acknowledge God any longer, God gave them over to a depraved mind, to do those things which are not proper," (Romans 1:26-28).
Homosexuality is cited as an example of the depths of human sinfulness when we reject God and His standard. Indeed, part of what makes homosexuality sinful is that it is "unnatural," i.e. opposed to the obvious design of men and women. God has a purpose for human sexuality, and this is not it! Elsewhere in the New Testament, homosexuality is listed among other sins from which Christians are to repent and turn from in coming to Christ:
"Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived; neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor homosexuals, nor thieves, nor the covetous, nor drunkards, nor revilers, nor swindlers, will inherit the kingdom of God. Such were some of you; but you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus Christ and in the Spirit of our God," (1 Corinthians 6:9-11).
"But we know that the Law is good, if one uses it lawfully, realizing the fact that law is not made for a righteous person, but for those who are lawless and rebellious, for the ungodly and sinners, for the unholy and profane, for those who kill their fathers or mothers, for murderers and immoral men and homosexuals and kidnappers and liars and perjurers, and whatever else is contrary to sound teaching, according to the glorious gospel of the blessed God, with which I have been entrusted," (1 Timothy 1:8-11).
So, while homosexuality is not a primary focus for most of the Bible, it is plainly identified in several places as a sin. What's more, it is a clear violation of the specific, positive sexual ethic that is a major focus throughout Scripture.