Unlike many today, the writers of the New Testament did not think the book of Leviticus out of date or irrelevant. Paul uses Lev 18.5 as a crux of some of his arguments on justification by faith (Rom 10 and Gal 3). Also, in Peter’s first epistle he refers to Lev 19.2 in regards to how christians should live. Both here in Leviticus and in Peter the command assumes a relationship, it is not the basis of the relationship. That’s to say, our relationship to God doesn’t come about by our being holy, but our being holy comes about because of our relationship to God.
We can take a few things from this. First, a good self-examination is in order. Are we holy as God is holy? Is this our pursuit and desire? As we pursue this, and fail and struggle at it, we need to turn our eyes again and again to Christ, who is our holiness. Second, when we think about those who do not yet know Christ and God’s forgiveness, their greatest need is not to act better, to be more holy; that’s the cart before the horse. Their greatest need is Christ, and then they can worry about being holy, not to gain acceptance with God, but to seek the please God (2 Cor 5.9).