Do morals change?
The modern moral law should be applied to Old Testament times and to Christendom. We should not excuse immoral behavior just because it happened in a previous age. Some examples...
The Church has had a wrong view of the body and the physical realm since the early centuries because they were strongly influenced by various wrong philosophical systems such as those of Plato, Aristotle, Augustine, St. Thomas Aquinas.
This kind of thinking appeared even in Old Testament times. Later, near the beginning of the Christian era, the Jewish philosopher Philo taught a duality between the evil physical world and the good spiritual world.
I was taught by fundamentalist evangelical Protestant Christians that the conscience of each person is fully-formed at conception containing God's law. This is false. The conscience is a capability in humans to distinguish right from wrong but the content of the conscience must be developed via moral training. This is why it is so important for Christians to study the virtues.
Sadly, our modern culture fills the conscience with garbage via TV, movies, music, peers, books, anti-Christian public school teachers, anti-Christian parents, and worse, the anti-Christian culture at-large including the leaders, activists, politicians, and other spokespeople.
And sadly, many Christians have flawed ideas about right and wrong, thinking that small sins (venial sins) are as bad as mortal sins. And they teach that the 10 commandments are general rules for Christian behavior. This is absurd! the 10 commandments list very serious mortal sins leading to eternal damnation in hell.