How the Christian Bible we have today came into existence is a long, convoluted story, as can be expected. It is an ancient text that is being applied to life thousands of years after it was written. No one ever kept all the laws in the Christian Bible. The ancient Israelites did not practice any of the Christian rituals such as Holy Communion. And Paul did not believe in forcing the gentile Christians in keeping the Law of Moses.
The Bible was written thousands of years ago, in a very different context for a very different people than exist today. It was written over the course of thousands of years so that the Law of Moses no longer applied to the people at the end of the New Testament.
Can the Bible be trusted? I think each person has to decide for themselves. Over the last thousand year, the Bible has been translated countless times into every language on earth. Translations built on translations. Bart D. Ehrman, starting out as a fervent evangelical Christian seeking to prove his faith through scholarship, discovered how the the meaning of the New Testament was changed word by word. Google his name; he has blogs and books online.
For a good book on how and why the Old Testament was written, see Robert Elliott Friedman’s book.