Interpreting Scripture And Feminine Hygiene
I have three basic principles I use when I interpret the bible.
1. Christo-centric Hermeneutics: This is the philosophy of biblical interpretation that says that the purpose of all scripture is to reveal Christ.
Christo-centric: "Making Christ the center, about whom all things are grouped, as in religion or history; tending toward Christ, as the central object of thought or emotion." 
Hermeneutics: "The theory and methodology of interpretation, especially of scriptural text." 
If we believe what Jesus said, then we know that the bible is all about Jesus. That's obvious in the New Testament, But, you may ask, what about the Old Testament? Jesus himself says the Old Testament is about Him. - "You search the Scriptures, for in them you think you have eternal life; and these are they which testify of Me." John 5:39.
2. Line upon line
Understand the easy stuff first, then move on to the harder parts. Again, the bible explains this in Isaiah 28:9-10: 9 "Whom will he teach knowledge? And whom will he make to understand the message? Those just weaned from milk? Those just drawn from the breasts? 10 For precept must be upon precept, precept upon precept, Line upon line, line upon line, Here a little, there a little."
Some parts of the bible are very clear. Other parts are more obscure. If there is something we don't understand, we go back to what we do understand, and start there. Sometimes, it's necessary to set something aside and come back after we have more knowledge. As we grow in wisdom and maturity, so will our understanding of scripture.
3. Guidance of the Holy Spirit
In John 14:26 Jesus says, "But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things ..." God, in the person of The Holy Spirit, wants to build a relationship with us. When we study the scriptures, it's an opportunity for God to speak to our heart and soul. If there's something you don't understand about scripture ... Ask God, and expect an answer.
James 1:5: If any of you lacks wisdom, he should ask God, who gives generously to all without finding fault, and it will be given to him.
I was surprised at how well this works when I was once "randomly" assigned the following scripture to write a devotional about: Leviticus 15-16. (I put the word "randomly" in quotes, because I'm pretty sure God arranged this.)
Now, Leviticus 15 focuses on the Levitical laws about various bodily functions and fluids, including feminine hygiene.
Consider: Leviticus 15:19: When a woman has a discharge, if her discharge in her body is blood, she shall continue in her menstrual impurity for seven days; and whoever touches her shall be unclean until evening.
What was I supposed to do with that? Here I was a single man, asked to write a devotion about something I have little knowledge of, on a delicate topic for a very socially conservative audience. Oh, yeah, I could move up a few verses and talk about "wet dreams". That would be a real hit! And so, I thought I'd move on to Chapter 16. It was about Yom Kippur. ... I could focus on that and simply ignore the part before it.
Except, when I prayed about The Holy Spirit told me, "I put those laws before Yom Kippur for a reason. I want you to write about that." So, I prayed and I researched and I looked and I applied the principles.
One of the first things I discovered was that "Unclean" is not actually a moral judgement. It is simply an acknowledgement that something is unhealthy. It was one of the things that lead me to understand that sin is not simply moral failure (The Greatest Sin).
What follows is the Christo-centric, research based, Holy Spirit led devotional I wrote regarding the "Levitical Laws on Hygiene"
There is certainly nothing morally wrong with natural body functions. However, discharges of various bodily fluids can certainly be unhealthy. If we don't take care of our personal hygiene, we can become ill and possibly infect others. Sin is like this. In this passage, God uses the physical as a metaphor for the spiritual. In our natural state we are all unclean and cannot stand in the presence of a Holy God. Furthermore, if we are not careful, we can spread this problem to others.
However, God does not want us to die in our natural, unclean, state before Him (Leviticus 15:31). So, he provides a way that we can be clean and approach Him. On the Day of Atonement (Yom Kippur) God tells Moses that blood is to be shed for the remission of the peoples sins (Hebrews 9:22).
While water may wash away infection, the blood of animal sacrifices cannot wash away sin (Hebrews 10:4). The sacrifices made by the Levitical priesthood were a picture of the sacrifice to be made by Jesus on the Cross (Hebrews 9:11-15). God always provides a way for those who are willing to be cleansed, so that they can stand in His presence, and not die in their natural unclean state.
Father in Heaven, you are a Holy God, and we thank you that while on our own we are not "clean enough" to stand in your presence, you have provided us with the cleansing blood of your Son, Jesus. Now that you have cleaned us, bring us into your Holy presence and reveal yourself to us. Amen.