Two verses in Leviticus (Leviticus 18:22 and 20:13) seem to prohibit male homosexual sex, although we will see later that the meaning of the verses is actually very restricted. But are these regulations binding to Christadelphians?
The answer is no. Christadelphians are not under the Law of Moses.
Before this faith came, we were held prisoners by the law, locked up until faith should be revealed. So the law was put in charge to lead us to Christ that we might be justified by faith. Now that faith has come, we are no longer under the supervision of the law. (Galatians 3:23-25, NIV)
But could it be that we are bound by the "moral" parts of the Law of Moses, and faith only releases us from the "ritual" parts? Again the answer is no. You are bound by all of the Law, or by none of it.
For whoever keeps the whole law and yet stumbles at just one point is guilty of breaking all of it. (James 2:10, NIV)
The prohibitions against male-male sex come from the same part of the law that prohibits sex with a menstruating woman (Leviticus 18:19) and paying a hired man monthly rather than daily (Leviticus 19:13). If, contrary to Galatians 2:23-25, we are still bound by the "moral" aspects of the law, then these regulations, clearly moral rather than ritual, should still be binding. No Christadelphian feels that way. No Christadelphian believes that we are still under the law of Moses.
We still have to think about what Leviticus actually means. Although the law of Moses is not binding on us today, it was binding on the people of God between Moses and Christ. Understanding Leviticus 18:22 and 20:13 is important when looking for Biblical affirmation of same-sex relationships in the Old Testament, and through the Greek translation of the Old Testament, the Septuagint, Leviticus 18:22 and 20:13 may have influenced Paul when he wrote 1st Corinthians and 1st Timothy. Understanding Leviticus can help us understand what Paul meant.
Do not lie with a man as one lies with a woman; that is detestable (Leviticus 18:22, NIV)
If a man lies with a man as one lies with a woman, both of them have done what is detestable. They must be put to death; their blood will be on their own heads. (Leviticus 20:13, NIV)
In most English translations, these verses seem to utterly forbid all forms of male-male sex. However, the verses are not actually that general. If it was general, why is the phrase "as one lies with a woman" present in both verses? Why don't the verses just say "You will not lie with a man", or "You will not lie carnally with a man"? (See Leviticus 18:20 in the KJV.)
The Hebrew idiom used here, literally translated "the lyings of a woman", is difficult to decipher. It is related to another phrase, "the lyings of a man" (see Numbers 31:18). In the Babylonian Talmud, "lyings of a man" is contrasted with other forms of sexual activity between men, indicating that it is not a blanket reference to all sexual activity. "The lyings of a man" is restricted in meaning, and so "the lyings of a woman" is also restricted in meaning. The evidence indicates that it means anal sex,1 an activity that even today is not a feature of all male-male sexual relationships.2
With this knowledge of Leviticus, we can now move onto two passages in the New Testament, 1 Corinthians & 1 Timothy.
1 Olyan, Saul M 'And With a Male Your Shall Not Lie Down the Lying of a Woman': On the meaning and significance of Leviticus 18:22 and 20:13 Journal of the history of Sexuality, Volume 5 pp 179-206, Boyarin, Daniel Are the any Jews in the history of sexuality Journal of the History of Sexuality Volume 5 pp 333-355 and Walsh, Jerome T Leviticus 18:22 and 20:13: Who is Doing What to Whom? Journal of Biblical Literature, 120/2 (2001) pp201-209
2 Sexual Behaviour in Britain by Wellings et al, pp218-226
Come, you who are blessed by my Father; take your inheritance, the kingdom prepared for you since the creation of the world
Matthew 25:34, NIV