“For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord” (Romans 6:23).
There is no doubt that since Christianity began it taught its members to be holy as God is holy. This has sometimes been reduced in people’s minds to referring only to morality, but holiness is not just proper external behavior, it also has to do with the state of a person’s heart, and in fact their very being including their relationship with God. Sometimes Christians reduce the sense of holiness to sexual activity, something which was influenced by ideas presented early on in Christianity by dualists who despised the body and marriage, treating any sexual desire as a disease (St. John Cassian calls it such in his Institutes, though admittedly he is writing for monks not to all Christians). This abhorrence of anything sexual ultimately denies the goodness of creation and is at odds with the Genesis story of God creating humans male and female as well as with the Gospel truth of the incarnation where Jesus is a male (not an androgynous being). Today, as in every generation of Christianity, we see these ideas manifesting themselves, in our times especially in claims which make homosexuality to be veritably THE unforgivable sin. In the book In the World, of the Church, Paul Evdokimov notes:
Berdiaev [Nikolai Berdiaev, a 19th century Russian religious and political philosopher] stressed with reason that the Gospel is infinitely more severe toward wealth, exploitation, and social disorder than toward any sexual failing. The real problem of social obligation has been repressed and replaced by a veritable obsession with matters sexual, even up to our time. According to the Gospel, it is the rich who will not enter the Kingdom, while repentant prostitutes enter ahead of the righteous and their influence. ( pg. 87)
We are so often concerned with or obsessed by the sins of others, while holiness tells us when it comes to sin to specifically look at ourselves. Christianity is a self-denying religion, but only when it comes to sin does it traditionally tell us to look at ourselves and judge rather than looking at and judging others.