Sorry for the long response, here’s a summary:
· Jesus is a reliable source for Christian marriage.
· Natural does not equal sanctified.
· Galileo is instructive for why we can’t impose extra-biblical ideas on scripture
First, let me say I have no moral high ground to stand on. I, as much as anyone else, am a sinner deserving of God’s judgment. But thanks be to God that while we were yet sinners, Christ died for us (Romans 5:8). I’m only quoting scripture because this is an intramural debate among Christians. It seems reasonable that Christians examine what scripture says on a particular topic when discussing whether Christians should adopt one position or another.
Second, Jesus affirmed the entire Old Testament law (Matthew 5:17), including the Torah (of which Leviticus is included) (John 5:46). Jesus addressed the contemporary arguments about marriage by affirming God’s design for marriage by quoting Genesis chapter 1 (Mat. 19:3-12). I suspect the reason Jesus did not specifically mention homosexuality is that it is unlikely Jews were openly practicing homosexuality in first century Palestine because in their zeal they were quick to execute anyone caught in sexual sin (John 8:4). Jesus forgave the adulterer but commanded her to leave her life of sin (Jn 8:11). He didn’t excuse her sin because it was a naturally occurring desire for companionship.
As an aside, Jesus didn’t say anything about income inequality but that does not mean he would necessarily bless legal regimes which permit ever-expanding inequality. (I’m not arguing for or against, just using as an example).
Third, just because something occurs naturally does not mean it is a sanctified desire. By nature, I am inclined to all kinds of sinful actions, including sexual immorality, but that does not mean God blesses it. Rather, we are to abstain from sinful desires (1 Peter 2:11) and put to death (metaphorically speaking) the misdeeds of the body (Romans 8:13).
Finally, the Bible does not and has never taught the geocentric model. The story of Galileo is an example of the church adopting the prevailing scientific/cultural attitude of its day (Ptolemaic astronomy) and imposing it on the Bible rather than allowing the Bible to speak for itself. This is exactly what proponents of redefining Christian marriage are attempting to do.