Why is homosexuality a sin?

No such thing as sin.

In your question above, you mention mosaic law but seem more interested in what the new testament states. The scripture that best sums up what you are asking is 1 Corinthians 6:9-10. It says,

"9 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 [a]effeminate, nor homosexuals, 10 nor thieves, nor the covetous, nor drunkards, nor revilers, nor swindlers, will inherit the kingdom of God." NASB

What is usually argued is the translation was misinterpreted over the years, homosexuality was added. So if you look at the original greek, the greek word arsenokoites refers to same-sex couples. It correctly translates to those who practice homosexuality.

Paul, the writer of Corinthians, can be no clearer in his statement. The next arguement would be then, who gives Paul the authority to make this statement. The original apostles and the early church accepted Paul and his authority. If you believe that the bible is the inspired word of God, then that is your answer.

If you really want to know, why not do some study of your own rather than the opinions of others. Most people will pick and choose what to believe by regarding or disregarding scripture based on which scripture supports or doesn't support their position.

Condemnation of homosexuality is found in both the Old and New Testament:

Old Testament: Genesis 19:1-29; Leviticus 18:22; 20:13; Deuteronomy 23:17; Judges 19:22; 1 Kings 15:11-12; 22:46; Ezekiel 16:49,50;

New Testament: Romans 1:18-32; 1 Corinthians 6:9-11; 1 Timothy 1:9-10; 2 Peter 2:4-8; Jude 1:7.

The question seems confused - but here is the answer to the main question.

Sin - by definition - is acting contrary to the express will of God. So: homosexual behavior is sin for the very same reason that ANY sin is sin. That reason: because God has informed us that he disapproves of such behavior.

Now: if you want to know why God has deemed such behavior to be sin: we're at a loss. Typically (there are exceptions), God does not teach us *why* a particular sinful behavior is wrong. Typically, God only teaches us *that* it is wrong.

Note: the New Testament clearly and repeatedly condemns homosexual behavior. So - for Christians at least - the condemnation of that same behavior in the Old Testament it is less relevant than its condemnation in the New Testament.

- Jim, http://www.bible-reviews.com/

because it defeats Gods purposes for the sexes - the oneness factor

and it is prohibited in both testaments

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Mat 19:4 And Jesus answered and said unto them, Have ye not read, that he which made [them] at the beginning made them male and female,

Mat 19:5 And said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh?

Mat 19:6 Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder.

1Cr 6:9 Don't you realize that those who do wrong will not inherit the Kingdom of God? Don't fool yourselves. Those who indulge in sexual sin, or who worship idols, or commit adultery, or are male prostitutes, or practice homosexuality,

1Cr 6:10 or are thieves, or greedy people, or drunkards, or are abusive, or cheat people—none of these will inherit the Kingdom of God.

Because it is repeated in the New Testament several times

here is one

1 Corinthians 6: 9 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 homosexuals, nor sodomites, 10 nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit

the kingdom of God

It's not being homosexual which is a sin.

It's the misusing of sexual activity.

Sex is intended for procreation of children.

Raising children requires commitment of marriage.

Children need both male & female parents.

That's so they can grow up as healthy members of society.

God says to go visit Lot and his daughters and you will soon learn why.

It wasn't considered a sin by the Christian Church until the Bible was mistranslated in 1611.

It is the only common hatred that is allowed today.

It's a sin because we h0mo's are hotter and cleaner then everyone else