But why do they spend more time talking about tithes, offerings, Moses, David, Abraham et al?
The Psalms are the most read and used part of the Bible. And that's also the Old Testament.
The Christian church teaches mainly out of the writings of Paul. It's why most Christians refer to themselves as New Testament Christians.
And the reason they bring up tithes is because the Christian church are thieves because tithing has nothing to do with money (and they know that).
And they damn sure don't talk about Moses because Christianity teaches all of the Mosaic laws are done away with. It's why Christians don't keep the Sabbath, don't keep any of the feast days (passover, first fruits, tabernacles, dedication), and don't keep the new moon.