If you want to understand the NT, BOM, or even D&C, you need to understand the OT. Jesus was a marginal Jew, after all, and it helps to understand Judaism before understanding what came out of Judaism. You might want to study Judaism itself for a while to get an idea of how the OT affected the people that lived in Jesus' day. Modern Judaism is an outgrowth of the Pharisee movement, so you need to perform some historical regression from modern times back to the OT, but it is extremely interesting. It will take a while, but you will probably get more out of the NT and BOM in the long run.