Many people in favor of gay marriage claim that homosexuality is not addressed directly by Jesus in the New Testament. So why is it still a sin? If you have never read the Bible, here is an explanation:
The Old Testament has many "contracts" with man. These are known as covenants. Some are permanent, but others are listed as temporary. It's the Old Covenant in the Old Testament that was fulfilled by Jesus in the New Testament. The Old Covenant consists of the civil/ceremonial laws of the Jews. However, civil/ceremonial laws are very different from the moral laws in the Old Testament.
Examples of the civil or ceremonial laws might include this: Things like sacrificing lambs on Passover, it means they can't be eating pork or shellfish. Most of these civil or ceremonial laws are in the book of Exodus and Leviticus.
It is the moral laws, such as the 10 commandments and all other moral laws throughout the Old Testament that are still very, very, very intact to this day. These moral laws include murder, adultery, sexual immorality, theft, false testimony, slander.
So, The reason why homosexuality in the Bible is still a sin is because the moral laws are still intact from the Old Testament. In addition to just the Old Testament, Jesus and Peter also preached against sexual immorality as a whole. Notice the root word of immorality is moral. That means that nothing I said is being taken out of context to support a messed-up "narrative".