Robert Plummer’s contribution to the 40 Questions Series is a great book for grasping the basics of hermeneutics, or properly interpreting the Bible. I found the following quotation of particular help, since the question about Christians not adhering to Levitical laws is an all too common question.
Many supposed inconsistencies of Christian morality (for example, the charge that Christians pick and choose their morality from the Bible) are explained by understanding the provisional and preparatory nature of the civil and ceremonial laws of the old covenant period. The parallel is not exact, but imagine how foolish it would be for someone to raise the accusation, “Millions of people in every state of the Union are flaunting the Constitution! You don’t really believe or obey your Constitution, which clearly states in the Eighteenth Amendment:
“The manufacture, sale, or transportation of intoxicating liquors within, the importation thereof into, or the exportation thereof from the United States and all territory subject to the jurisdiction thereof for beverage purposes is hereby prohibited.”
To which we would reply, “Yes, that amendment once was the law of the land, but it was superceded by the Twenty-First Amendment, which begins, ‘The eighteenth article of the amendment to the Constitution of the United States is hereby repealed.'”
The Bible is not a policy book, with each page giving equally timeless instruction. Yes, “Every word of God is flawless” (Prov. 30:5). Nevertheless, the Bible is more like a multivolume narrative, in which the later chapters clarify the ultimate meaning and sometimes the temporary, accommodating nature of earlier regulations and events (e.g., Matt. 19:8).40 Questions About Interpreting the Bible, 169.