Those who have read the Old Testament know that Leviticus is not the most interesting of all books. It is full of rules and regulations about how to be holy for God. This book is often used from the holiness tradition to tell people what they do wrong and how to live righteously. Honestly, I rarely hear this book used in a positive way, but rather in a legalistic way.
On Sunday night, I was reading through the weekly readings in my Mosaic Bible, which included Leviticus 19:18. I was surprised to see "love your neighbor as yourself" there. For one reason or another, I never remember hearing that this was ever in the Old Testament; it's always quoted in reference to Jesus.
I think it's significant that love is explicitly prescribed in the Old Testament, particularly in a book that is focused on rules. This should remind us that we need to view all rules in the context of love.
Also, since we're on the topic of Leviticus, I think it is often misused to support legalistic holiness. From my studies of it, it seems more appropriate to view the various rules (which are often strict and numerous) as a way of setting the Israelites apart from the rest of the world. The rules themselves are not necessarily holy, but rather the process in what they mean. If we are to live a holy life, that does not necessarily mean living out Leviticus literally, but rather in process: What sets us, as Christians, apart from society, particularly emphasizing love?