Under the Law of Moses, homosexual acts were prohibited. Leviticus 20:13 says “if a man lies with a male as with a woman, both of them have committed an abomination”. Sometimes Christians will look to this part of the Bible for moral direction about sexual ethics and take Leviticus 20:13 as a clear and unequivocal condemnation of homosexual acts. One common response to this is to point out the apparent inconsistency in requiring this part of the Law be kept, whilst other parts of the Law (such as the prohibitions regarding pork and shellfish — Leviticus 11:2-12 — are ignored). It might appear that Christians are picking and choosing which commands to follow.
However to understand the Christian perspective, one needs understand why Christians reject the food laws in the Law of Moses. Christians believe that Jesus was the fulfilment of the Law. Jesus says “Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them” (Matt 5:17). This is taken to mean that everything in the Law that pointed forward to Jesus has been fulfilled and therefore have served their purpose. These are generally understood to be the ceremonial parts of the Law, particularly the laws about ritual separation. The food laws in Leviticus 11 are understood to fall into this category of ceremonial, because they are accompanied by the words “Consecrate yourselves therefore, and be holy, for I am holy” (Leviticus 11:44). Other laws are understood to be moral laws and are not understood to have a temporary symbolic purpose, but a lasting moral purpose. Amongst these are usually included the laws of sexual conduct found in Leviticus 20.
This distinction between ceremonial and moral laws is useful as far as it goes but needs supplementing. The apostle Paul argued that believers are not made righteous by obeying every command in the Law (which he deemed almost impossible); believers are made righteous through faith apart from the Law (Romans 3:21). Christians, therefore, do not seek to keep the commandments as a way of earning salvation. Instead, Christians believe they are saved freely by the grace of God and try to act in ways pleasing to him in response to this grace. The question for Christians then as they consider ethical issues is not “can I find a specific command for or against such-and-such?” but “is such-and-such pleasing to God or not?” When considering the question of homosexual acts, Christians try to understand what is pleasing to God by considering the whole Bible. Part of that consideration might be the Law of Moses, which has some strong words against homosexual acts, but by itself this is insufficient as other things are also strongly condemned.
Usually when Christians consider sexual ethics, they will start with the teaching of Jesus. Jesus said that God specifically created humans to be male and female (Matthew 19:4) and this was the basis of the institution of marriage (v5). For Jesus, sex outside of marriage or before marriage was illicit (v9). So Christians see Jesus as giving a strong indication that God’s intention from the beginning of creation was that sex should only happen within the context of a committed and exclusive heterosexual relationship. This teaching seems to be corroborated by Paul, who condemns homosexual acts (see 1 Corinthians 6:9; 1 Timothy 1:10; also Romans 1:27).
The Bible never condemns having a homosexual orientation, but when Christians look at the whole Bible there seems to be strong indicators that homosexual acts are prohibited.