Thank you for this question, Christopher, and for being part of this site!
These are really significant issues you raise.
There are some ways in which all sins are alike, and ways in which sins differ from one another, and I think this applies to the forms of sexual sin we encounter in ourselves and in others. So it is true to say that all sins are alike in some ways: all fall short of the glory of God; all are expressions and evidences of fallen sexuality that is common to us all. This means that none of us can feel proud for not having fallen into certain forms of sexual sin, or look down on those who have. We are all alike fallen in this area of life. The gospel levels the playing field. We’re all in this together, irrespective of what temptations we experience and what temptations others experience. One of the mistakes I think the church has sometimes made is in treating homosexuality in a disproportionate way — singling it out for regular condemnation while not necessarily treating heterosexual sin as seriously. It is significant that the references to homosexuality in the Bible always come in the context of other forms of sexual sin also being warned against. (One exception to this might appear to be Romans 1, where Paul talks about men and women exchanging natural relations with the opposite sex for unnatural relations with the same sex. But even here he immediately follows it up at the start of ch.2 with a condemnation of those who look down on these sins but do not adequately come to terms with their own.) Truly understanding our common sexual brokenness should actually make Christians the most compassionate people on the planet.
But that is not to say all sexual sin is the same. Genesis 1-2 shows us God’s blueprint for human sexuality (echoed by Jesus in Matt. 19:3-6): one man and one woman within the covenant of marriage. It is therefore fair to say that certain forms of sexual sin represent a greater departure from this blueprint than others. Promiscuity is a further departure than does fornication. Homosexuality a greater departure than adultery. We see this reflected in the codes on sexual behaviour in Leviticus 18 and 20. In both cases sexual sins are listed in a clear progression, one which takes us step by step away from God’s design.
We need to hold both these aspects of the issue together at the same time. A common mistake in evangelism to our gay friends is to talk about the difference before we have sufficiently expressed the universality of our sexual fallenness. So I think it is generally best to start by showing how the Bible’s teaching is deeply challenging and humbling to all of us, before ever then talking about one particular type of sexual sin.
Thanks again for joining us and asking great questions!
Wishing you every blessing today,