(All references are from the New King James Version.)
Genesis 1-2 recounts how God created the world and set it in order. It is clear from this passage that the natural order is for a man to be physically united with a woman, not another man.
27So God created man in His own image; in the image of God He created him; male and female He created them.
24Therefore a man shall leave his father and mother and be joined to his wife, and they shall become one flesh.
Genesis 18:16-19:26 recounts the story of the destruction of Sodom and Gomorrah.In Genesis 19:4-8, it is clear what sin Sodom committed to merit its destruction:
Now before they lay down, the men of the city, the men of Sodom, both old and young, all the people from every quarter, surrounded the house. 5And they called to Lot and said to him, “Where are the men who came to you tonight? Bring them out to us that we may know them carnally.”
6So Lot went out to them through the doorway, shut the door behind him, 7and said, “Please, my brethren, do not do so wickedly! 8See now, I have two daughters who have not known a man; please, let me bring them out to you, and you may do to them as you wish; only do nothing to these men, since this is the reason they have come under the shadow of my roof. ”
In the New Testament, Jude 7 reinforces Sodom’s punishment, explicitly stating that the Sodomites were punished for sexual perversion, not simply for being inhospitable:
7 [A]s Sodom and Gomorrah, and the cities around them in a similar manner to these, having given themselves over to sexual immorality and gone after strange flesh, are set forth as an example, suffering the vengeance of eternal fire.
In Leviticus, God lays out in detail what is right and wrong in the area of sexuality.
Leviticus 18:22 specifically prohibits homosexuality:
22You shall not lie with a male as with a woman. It is an abomination.
Leviticus 20:13 adds to that:
13If a man lies with a male as he lies with a woman, both of them have committed an abomination. They shall surely be put to death. Their blood shall be upon them.
In the New Testament, homosexuality is considered a serious sin as well. Jesus reiterates the Old Testament teaching that marriage is exclusively between one man and one woman in explaining why divorce is a sin. Matthew 19:4-6 states:
4And He answered and said to them, “Have you not read that He who made them at the beginning ‘made them male and female,” 5and 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’? 6So then, they are no longer two but one flesh. Therefore what God has joined together, let not man separate..”
In Romans 1 the author illustrates how sin begets more sin. Man started out by suppressing the truth of God, fell deeper into sin by worshipping men and animals, fell further into sexual immorality, and spiraled down even more into homosexuality.
26For this reason God gave them up to vile passions. For even their women exchanged the natural use for what is against nature. 27Likewise also the men, leaving the natural use of the woman, burned in their lust for one another, men with men committing what is shameful, and receiving in themselves the penalty of their error which was due.
In 1 Corinthians there is a list of groups described as unrighteous, and this includes homosexuals. 1 Corinthians 6: 9-10:
9Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, 10nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God. [Emphasis added.]
But God gave homosexuals, just like other sinners, hope for redemption:
1 Corinthians 6:11:
And such were some of you. But you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus and by the Spirit of our God.
In order to guard against sexual immorality, the New Testament clearly defines marriage as between a man and a woman in 1 Corinthians 7:2:
2Nevertheless, because of sexual immorality, let each man have his own wife, and let each woman have her own husband.
1 Timothy 1: 9-10 lists groups of sins, including homosexuality:
9[K]nowing this: that the law is not made for a righteous person, but for the lawless and insubordinate, for the ungodly and for sinners, for the unholy and profane, for murderers of fathers and murderers of mothers, for manslayers, 10for fornicators, for sodomites, for kidnappers, for liars, for perjurers, and if there is any other thing that is contrary to sound doctrine. [Emphasis added.]