Wow, talk about irony. You are showing your ignorance by not knowing that it is all part of the same Bible. Have you never been in a church that preached from the OT?
You don't understand something very vital about the Bible, and obviously have never read parts of it.
I certainly have been in a church that preaches from the Old Testament as well as the New. It illustrates very clearly what God's standards are, but the Mosaic Law has been completed. When you went to school, the teachers and administrators gave you and your parents a student handbook with a set of rules that you were expected to follow while you were in school. You were told what clothes you could wear, what you could bring with you to school, when you had to be in the classroom, when you could eat, when and how you could play and when you had to do schoolwork. You were given instructions on how you had to behave toward your fellow students. Failure to follow these instructions resulted in discipline, ranging from a reprimand to expulsion from school.
After you graduated, did any of your teachers come over to your house and check out what you were doing, what you were wearing, when you ate, when you went to work, how you behaved towards other people? No. They expected that you learned important lessons from your stay in school about prioritizing work and play and how to behave towards others. It is such with the Mosaic Law and Jesus Christ. He didn't lower the standards of behavior, He raised them. The Law says, don't commit adultery. Jesus said you commit adultery when you so much as look and desire. The Law says don't murder. Jesus says don't even hate. The difference is, the Law provided penalties for violations while Jesus paid the penalties Himself. We're not under the Law anymore, so when you insist we should be stoning people for wrongdoing, you're simply wrong. In fact, if we expect following the Law to do us any good, we have to follow ALL the law, not just the parts that condemn homosexuality but the parts that specify how many types of fabric can be in our clothes and how to trim our beards.
