Contrary to what you may have believed, the Old Testament is not the only part of the Bible that deals with homosexuality. There are several New Testament passages that also contain clear warnings against this type of behavior. What is likely the most clear warning against homosexual activity in the New Testament comes from Romans 1. For sake of brevity, I will quote the relevant sections:
So I am eager to preach the gospel to you also who are in Rome. For I am not ashamed of the gospel... in it the righteousness of God is revealed... For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppress the truth... For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse. For although they knew God, they did not honor him ... but they became futile in their thinking, and their foolish hearts were darkened. Claiming to be wise, they became fools, and exchanged the glory of the immortal God for images resembling mortal man and birds and animals and creeping things.First off, I have to say I feel horrible for chopping up that passage like I did. Please, read the entirety of Romans 1 for yourself, or else the heart of Paul's message may be lost. At least, read the entirety of what is quoted here before continuing.
Therefore God gave them up in the lusts of their hearts to impurity, to the dishonoring of their bodies among themselves, because they exchanged the truth about God for a lie and worshiped and served the creature rather than the Creator, who is blessed forever! Amen.
For this reason God gave them up to dishonorable passions. For their women exchanged natural relations for those that are contrary to nature; and the men likewise gave up natural relations with women and were consumed with passion for one another, men committing shameless acts with men and receiving in themselves the due penalty for their error... they not only do them but give approval to those who practice them. (Romans 1:15-32)
Like all other passages we have dealt with, we must first look at the context. Paul (the author of the letter to Romans) starts this section by saying that he was eager to preach the gospel. He then lists all of his reasons why he is eager, each beginning with "for." The last reason is quite long, but its basic point is not difficult. That is, God's wrath is being revealed against the unrighteous and ungodly. Also, we have no excuse for leaving God's commands behind. Therefore, Paul feels that he needs to communicate this message, so that we aren't on the brunt end of God's wrath.
Paul is communicating the message that we must avoid sin, but the point of the whole book of Romans (as Martin Luther would scream from the mountaintop) is that Jesus' grace will overcome our sin. "There is therefore now no condemnation for those who are in Christ Jesus." (8:1) We must keep both ends of this message in mind when reading this passage.
Before Paul moves on in his point, he gives examples of the kind of depravity that humanity has sunk into, giving specific examples of the culture surrounding him. This is no abstract list, though. Paul is describing actions that people used to replace God's plans with their own.
As the Bible made clear from the very beginning, God has a very specific design for many aspects of our lives. In his 10 commandments, the very first one was that they should not make an image of God and then worship that image. This is at the very heart of every story in the Old Testament.
In fact, this concept is at the very heart of sin. Sin is determining that your own designs and desires are more important or more immediate than God's. Thus, we are placing an image, a replica, or a counterfeit in the place of God and his design. This is the very thing that Romans 1 describes.
Verse 25 says it all, "they exchanged the truth about God for a lie and worshiped and served the creature rather than the Creator, who is blessed forever!" The very heart of all sin is serving the creature (including ourselves) rather than the Creator.
The question that then raises is not whether some of the things we do are pleasurable or whether they feel right. In fact, if they never felt good, we would have no desire to do them. Instead, this is a declaration that there is something better.
If we serve anything besides God himself above God himself, we have counterfeited his design. We have a cheap version of the wonderful way he has arranged things. This is the very heart of this passage. If we want to replace God for something else, he'll let us. He'll also let us receive the consequences of those decisions...
...Unless we have faith in God's forgiveness. The rest of Romans explains this concept in great detail, and I would be merely wasting space if I were to lay it all out here. We have all sinned, but we can all be justified by God's grace alone, if we only have faith in him.
So how does this relate to homosexuality? It is listed as just one of many things that God will let us do if we want to. However, it is one of those many things that are a counterfeit of his design.
As with any cheap thing, homosexuality cannot withstand the pressure of life. It may seem good for a time, but it is only an imitation of the real thing that God has for each one of us. Like all of the other sins listed in this chapter, it declares our desire to replace God's plan with our own. But, we are without excuse. Let us not replace the truth of God with a lie. Instead, let us worship the Creator above his creation, and his purposes above our own.