Most Protestants do not seem to know anything much about the Old Testament. I've read the entire thing. Parts of it are a little peculiar, but that's because, or partly because we are in the 21st century, and (most of us are) American.
Enough said IMO
In any case, the most important thing IMO about the Old T is the Ark of the Covenant. Even a lot of Catholics don't know about that. I didn't either until a few years ago.
It was the beginning of the Church on Earth, meaning the one established by Christ himself. Basically, King David started being concerned that he himself lived in a palace and the Ark of the Covenant (a sacred "box" or tabernacle carried by the Israelites everywhere they went, a tabernacle where God would speak to them) did not have such a... worthy place. God spoke through a prophet and the prophet told David that God didn't need a house since He created the whole universe. But nonetheless, God approved of David building Him a house.
It's a fascinating story. It was in this House of God that God said He would "visit" man and listen to their prayers.