What does "loving one another" really mean?

Mark Smith posted this in the Classical Presbyterian blog comment section (scroll down to get the whole comment):
"[T]he church should be clear on what it considers the most important facets of Christ-like behavior. If you sat down and wrote out a list of Christ-like behaviors, I really don't think sexuality is even in the top 20."
He offered his start for such a list:

1. Loving God
   
2. Loving One Another
   
3. Giving of your time and talents
   
4. Being a member of a spiritual community

In response, I suggested:

I guess it rather depends on how you answer the question "what does it mean to love one another?" Biblically love is not some vague emotion or some undefined set of good intentions. It is deliberate actions defending a person's best interests. "But how do I do that," some ask. And God's answer is the law: do not steal, do not kill, do not covet, do not commit adultery... and that last puts sexuality right there as the way we live out number two on your "list of Christ-like behaviors."

Many years ago, the Presbyterian Church (USA) was introducing a new sexuality curriculum, God's gift of sexuality. As part of the roll out, they held training events in each Synod to help educators and ministers understand how this new curriculum worked and what it was all about. As an interested educator, I made it a priority to attend our Synod's event.

Ours was a pretty small group; no more than a dozen. But that was good because it gave us lots of quality discussion and interaction with the design team member who was introducing the curriculum to us. And the trainer was certainly excited about the product they had designed. It was a whole new approach to church-based sexuality education. For the first time, giving students accurate biological information was a goal of the church's educational plan.

And this curriculum was going to free youth from the narrow moralisms that had characterized sex education in the church in previous generations. They would find freedom knowing the God of love did not expect rote obedience to the letter of the law. Rather they could follow the Spirit and do the loving thing in each situation and relationship.

Being rather younger and more impertinent than I am today, I asked what in this curriculum would help the youth recognize what the loving thing was. How would they know what love was?

The presenter was not expecting that question. It never occurred to the design team to write lessons about what love is. Don't we all instinctively know how to love?

But we don't. One of the great tragedies of life is how people can try to do the right thing but still fail. People can want to love, can try to love, but can still end up causing great pain.

But God, who knows the end from the beginning, has told us what love is. That's the point of a passage like Romans 13:10: "Love does not harm its neighbor. So love does everything the law requires."

The Heidelberg Catechism puts it well (especially in the Christian Reformed Church translation) at Question 91:

What do we do that is good? Only that which arises out of true faith, conforms to God's law, and is done for his glory; and not that which is based on what we think is right or on established human tradition.

Put it this way: if the most important thing God has to say to us is "you shall love," then doesn't it make sense that would come with at least some instruction in how to do it? What kind of God would say "The most important thing I want you to do is love, but if you're looking to me for help with how to do that, you're going to be disappointed"?

But he has helped us with the meaning of love. He has given us some instruction in how to love. He has given it in his statutes, in his ordinances, in his law. And that law is not a burden to be escaped. It's a blessed gift to be received with thanks.