For an example of how biblical principles and MB come together, look at this passage from Mark 4:26-29 (NIV)
Clearly speaking to farmers in this chapter, since the entire chapter is about farming topics, Jesus is using what they understand to get them to understand a more fundamental principle than just something to follow as a way of life. If you look, he says that whether the farmer gets up early or sleeps late, the seed grows, implying that something else is at work here besides just hard work by the farmer. It isn't about working harder but in providing the right things for the seed to grow. He had already addressed how some seed doesn't grow because certain conditions aren't met and now seems to be saying that only the sowing is what matters.

But what he is really getting at is that if the right things are present, the seed will grow and it isn't the farmer's intent as to whether or not that happens. If the right nutrients are in the soil, the proper amount of water shows up at the right times and weather doesn't cause the crop to fail by getting too cold too soon or such things as that, the seed is going to grow almost as if the farmer had no part in it at all.

Of course farmers understand the need for preparing the ground and providing the proper things for the seed to begin to grow. They apply fertilizer, try to prevent weeds from overtaking the crops and monitor the weather. In some cases, crops such as oranges might require actions be taken to prevent damage by things that would cause the crop to fail. See what orange growers in Texas and Florida go through to save their crops when a freeze appears.

Dr Harley has identified the specific things that make a marriage grow. Emotional needs and all the rest can be summed up into his four promises we make to each other when we get married. They are Care, Protection, Time and Honesty. If those things are present, the marriage grows...

All by itself.

ENs are really the basic nutrients that romantic love needs to grow. Love Busters are those things that would stunt the growth or cause damage to the relationship and cause it to die. POJA and PORH are methods of ensuring that all is being done to protect the marriage that can be done. POUA is really the work that is put into the relationship. If these things are present then the marriage WILL grow. If they are not there, then the seeds of marriage will not produce.

Another thing to consider is this. The ultimate fruit of an apple tree is not an apple. It is another apple tree. Good marriages might abound but remain beneficial only to those in them. Great marriages become examples of what can be had by anyone if they ensure that the proper things are present in the relationship. Others will not only see it happen, but can learn from those in great marriages what it takes to make a marriage grow.

The first to see what a great marriage can do are the children that result from that marriage...

Another biblical principle at work in MB is found in John 5 where we read about the man who is lying beside the pool of Bethesda. Tradition in those days said that at times an angel would be sent by God to enter the pool. When that happened, the waters would be "stirred" and those who saw it would take action to get into the pool before the stirring had subsided. The first one into the pool would be healed of whatever happened to be his sickness. It didn't matter what that illness was, God would heal him.

Now Jesus encounters a man who has been lying beside that pool for many years. He asks the man if he wants to get well. The man begins to explain how he is helpless to get into the water alone and how others always get there first. He has a lot valid reasons why he hasn't been healed. But that isn't what Jesus asked him. He asked if he WANTED to get well.

When an infection was trying to eat the flesh from my body, the solution was to cut a gaping hole in my side. The answer to the problem caused even more pain, a protracted stay in the hospital and eventually another surgery to cut a piece of good flesh from elsewhere to fill the hole in my chest. I would have preferred to take a magic pill and be healed, but that wasn't going to save my life. There are no magic pills.

So when a marriage is broken and sick, the first question to answer is, "Do you want to get well?" It doesn't matter why it is sick or who is to blame or why it hasn't been healed already. The question is, "Do you want to get well?" If the answer is "Yes" then look at the passage in Mark 4 again to see what makes a marriage healthy.

The thing to remember about principles is that they are universally applicable. Methodology aside, the basic premise can be applied to all and not just a specific person or event. Methodology can be anything from planting seeds to ensuring that we only plant in soil that will allow the seed to grow and produce what we are looking for. Some got healed by entering the pool. One man was healed by a direct miracle that never happened before or since. The method wasn't what was in question, simply the principle of wanting to be well.

That's enough...

I can do this all day once I get started.